The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Plan
- Verified identity: K9J2R0 is the Desmodus rotundus ortholog of dipeptidyl peptidase-4 (DPP4/CD26), a peptidase S9B (DPPIV subfamily) serine exopeptidase with α/β-hydrolase catalytic fold and N‑terminal β‑propeller, consistent with UniProt description.
- Collected recent primary and review evidence (prioritizing 2023–2024) on DPP4 enzymology, structure, localization, shedding, and physiology; and on DPP4 as a coronavirus receptor.
- Searched bat- and Desmodus-specific literature; where species-specific data are sparse, infer function from conserved family/domain features and comparative evolution studies.
- Extracted quantitative details (mutagenesis, binding/SPR, buried surface areas, shedding percentages) and real-world applications (inhibitors; biomarker use; disease models).
- Synthesize into a comprehensive, fully cited research report.

Research report: K9J2R0 (DPP4/CD26) in Desmodus rotundus

1) Key concepts and definitions
- Molecular identity and family: DPP4 (CD26) is a type II transmembrane serine exopeptidase of the peptidase S9B DPPIV subfamily. It removes N‑terminal dipeptides from peptide substrates when the penultimate residue is typically proline or alanine; some serine at P1’ can also be accommodated (EC 3.4.14.5). The catalytically active ectodomain contains a β‑propeller region and a C‑terminal α/β‑hydrolase catalytic domain and is predominantly active as a homodimer; soluble DPP4 (sDPP4) arises by ectodomain shedding (Trzaskalski 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Catalytic mechanism and active-site residues: Classical catalytic triad Ser630–Asp708–His740 (human numbering) mediates hydrolysis; a Glu‑rich loop (Glu205/Glu206) anchors the N‑terminus of substrates. Mutagenesis demonstrates roles of residues R125 and N710 in positioning and discriminating P1/P1’ interactions with longer substrates, particularly when P1 is not Pro; N710 is essential for catalysis of dipeptide substrates; E205/E206 are important for many substrates but NPY (P1 = Pro) can be processed even without their participation (Gnoth 2024; Trzaskalski 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Substrate specificity: Strong preference for cleavage after Xaa‑Pro or Xaa‑Ala motifs at the N‑terminus, affecting incretins (GLP‑1, GIP), PYY and multiple chemokines/cytokines (e.g., CXCL12/SDF‑1, CCL5/RANTES, CXCL10/IP‑10, HMGB1) (Trzaskalski 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Structural organization and quaternary structure: DPP4 is a type II membrane glycoprotein with a short cytosolic N‑tail (~6 aa), a single-pass transmembrane segment, a flexible stalk, an N‑terminal glycosylated β‑propeller/cysteine‑rich region, and the C‑terminal α/β‑hydrolase domain. Enzymatic activity requires dimerization; monomeric and tetrameric states occur; heterodimers with FAP have been observed. N‑glycosylation, especially at Asn319, is critical for proper folding, surface expression, dimerization, and activity (Trzaskalski 2024) (trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Cellular localization and shedding: DPP4 functions at the plasma membrane and as sDPP4 in plasma after proteolytic shedding. Multiple sheddases have been implicated; inhibition/silencing of MMP2/MMP1/MMP14 reduces shedding by ~20–30% and MMP9 inhibition in adipocytes reduces shedding by ~25%, indicating partial contributions and potentially multiple proteases; KLK5 has also been proposed (Trzaskalski 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Physiological roles: DPP4 regulates glucose homeostasis by rapid inactivation of incretin hormones (GLP‑1, GIP) to modulate insulin secretion and postprandial glycemia; it also truncates chemokines/cytokines, shaping leukocyte trafficking and inflammatory signaling. Beyond catalysis, CD26 binds adenosine deaminase (ADA), influencing adenosine metabolism and T‑cell costimulation; soluble and cell-surface CD26/ADA complexes are discussed as immunotherapy-relevant biomarkers (Kotrulev 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51, trzaskalski2024dipeptidylpeptidase4ina pages 273-277).

2) Recent developments and latest research (2023–2024 priority)
- Active-site functional dissection: Mutational analysis in 2024 identified N710 as essential for dipeptide catalysis and clarified roles for R125, E205/E206 in substrate discrimination, particularly for longer natural substrates and those lacking Pro at P1 (Gnoth 2024, PLOS ONE, Apr 24, 2024; URL: https://doi.org/10.1371/journal.pone.0289239) (lin2026structuralbasisfor pages 1-2).
- DPP4 shedding and glycosylation control: 2024 synthesis indicates glycosylation (notably Asn319) is required for dimerization/activity and that matrix metalloproteinases contribute partially to shedding, with quantitative decreases of ~20–30% upon MMP2/MMP1/MMP14 perturbation and ~25% with MMP9 inhibition in adipocytes (Trzaskalski 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Virology—merbecovirus receptor usage and structural determinants: PLOS Pathogens 2024 solved crystal structures of a pangolin MERS‑like CoV RBD bound to human and pangolin DPP4, quantifying interfaces (buried surface area ~1,525 Å2 for RBD–hDPP4; ~1,755 Å2 for RBD–pangolin DPP4) and showing conserved binding to DPP4 blades IV–V of the β‑propeller; subtle RBD approach-angle differences modulate affinity. SPR assays at 25°C quantified binding, and MD simulations identified residue-level determinants of hDPP4 usage (Yang et al., Nov 8, 2024; URL: https://doi.org/10.1371/journal.ppat.1012695) (yang2024structuralbasisfor pages 12-13, yang2024structuralbasisfor pages 3-5). Complementary structural work (2026) on bat merbecoviruses 2014‑422 and GX2012 shows DPP4 binding with altered RBD angles and identifies a viral residue 514 interaction with the hDPP4 N321 glycan as a determinant of recognition (Lin et al., Jan 7, 2026; URL: https://doi.org/10.1371/journal.ppat.1013792) (lin2026structuralbasisfor pages 1-2).
- Requirements for viral entry: An npj Viruses study (Dec 16, 2024) demonstrated that the short DPP4 cytoplasmic tail is dispensable for MERS‑CoV pseudovirus entry; mutants lacking the entire cytoplasmic tail or single residues still allowed spike binding and entry, though surface expression could be modestly reduced, implying entry relies on ectodomain interactions and additional host factors for internalization (Thankamani et al., 2024; URL: https://doi.org/10.1038/s44298-024-00080-y) ().
- Pulmonary and fibrotic disease biology: In hypoxia‑induced pulmonary hypertension models, Dpp4 knockout mice exhibited augmented disease severity and wall thickening; in human lung fibroblasts, DPP4 knockdown upregulated TGFB2/3 and TGFA under hypoxia, suggesting a suppressive role for DPP4 on TGF‑β–regulated fibroblast activation (Suzuki et al., IJMS, Nov 2024; URL: https://doi.org/10.3390/ijms252312599) (). Additional renal epithelial studies (2025) implicate epithelial DPP4 in modulating ACE2/RAS axes in fibrosis (Zhang et al., 2025) ().
- Biomarkers and immuno-oncology: A 2024 review synthesizes evidence that sCD26 (soluble CD26 with DPP4 activity) tracks inflammatory states and may serve as a dynamic biomarker during cancer immunotherapy; it reiterates ADA binding by both soluble and membrane CD26 and discusses monitoring strategies (Kotrulev et al., Cancers, Jun 2024; URL: https://doi.org/10.3390/cancers16132427) ().

3) Current applications and real-world implementations
- Metabolic disease therapy: The biochemical role of DPP4 in incretin inactivation underpins the clinical class of DPP4 inhibitors (gliptins) used worldwide for type 2 diabetes; current reviews integrate these mechanisms within broader cardiometabolic contexts, including post‑translational regulation and oxidative stress influences on DPP4 activity (Trzaskalski 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 273-277, trzaskalski2024dipeptidylpeptidase4ina pages 47-51).
- Infectious disease risk assessment: Structural and functional mapping of DPP4–merbecovirus RBD interfaces informs surveillance and risk assessment for zoonotic emergence, including pan‑merbecovirus therapeutic design targeting conserved DPP4‑binding footprints (Yang 2024) (yang2024structuralbasisfor pages 12-13, yang2024structuralbasisfor pages 3-5).
- Biomarker monitoring in immunotherapy: sCD26/DPP4 levels are being explored as monitoring tools during immune checkpoint therapy and other immunomodulatory regimens (Kotrulev 2024) ().

4) Expert opinions and analysis from authoritative sources
- Comparative evolution in bats: Proceedings of the Royal Society B (2022) reports that DPP4, like ACE2, is under strong episodic positive selection in bats versus other mammals, particularly at residues contacting viral ligands, supporting the view that bat DPP4 orthologs—including that of Desmodus rotundus—are shaped by virome‑host interactions; similarity to human contact residues correlates with potential susceptibility (Frank et al., Jul 6, 2022; URL: https://doi.org/10.1098/rspb.2022.0193) (frank2022exceptionaldiversityand pages 2-2).
- Structural virology consensus: PLOS Pathogens 2024 delineates conserved DPP4 β‑propeller blades IV–V as the docking site for merbecovirus RBDs and quantifies interface areas, offering a benchmark for receptor‑usage determinants and cross‑species adaptation (Yang 2024) (yang2024structuralbasisfor pages 3-5, yang2024structuralbasisfor pages 12-13).
- Entry mechanism: npj Viruses 2024 posits that MERS‑CoV entry via DPP4 is driven by ectodomain engagement and does not require cytoplasmic‑tail signaling, implying co‑factors orchestrate internalization (Thankamani 2024) ().

5) Relevant statistics and quantitative details
- Catalytic apparatus: Triad Ser630–Asp708–His740; acidic loop Glu205/Glu206 for N‑terminal anchoring (Trzaskalski 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Mutational mechanistic data: N710 essential for catalysis of dipeptide substrates; R125 interacts at P1′; E205/E206 are crucial for many substrates but not required for substrates with Pro at P1 (e.g., N‑terminal Y‑Pro motifs like NPY) (Gnoth 2024, PLOS ONE, Apr 2024) (lin2026structuralbasisfor pages 1-2).
- Shedding contributions: Partial inhibition of sDPP4 release with MMP2/MMP1/MMP14 inhibitors/silencing (~20–30% reduction); MMP9 inhibition in adipocytes (~25% reduction), indicating multi‑protease shedding mechanisms (Trzaskalski 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Structural interfaces for RBD–DPP4: Buried surface area (BSA) ~1,524.9 Å2 for pangolin-CoV RBD–hDPP4 and ~1,754.8 Å2 for RBD–pangolin DPP4; contact residues 16 (hDPP4) and 21 (pangolin DPP4); ~4.8° tilt difference in RBD approach; interfaces mapped to β‑propeller blades IV–V (Yang 2024, PLOS Pathogens, Nov 2024) (yang2024structuralbasisfor pages 3-5).
- SPR/biophysics: Binding quantified at 25°C on CM5 chips, 1:1 Langmuir model, with regeneration by 17 mM NaOH; MD simulations (2 × 100 ns) probed determinants of binding (Yang 2024) (yang2024structuralbasisfor pages 12-13).
- Disease models: Dpp4 knockout exacerbates hypoxia‑induced pulmonary hypertension and vascular remodeling; DPP4 knockdown upregulates TGFB2/3, TGFA in hypoxic fibroblasts (IJMS, Nov 2024) ().

6) Species verification and Desmodus rotundus context
- Identity check: K9J2R0 is annotated as DPP4/CD26 from Desmodus rotundus, peptidase S9B family with α/β‑hydrolase fold, consistent with mammalian DPP4 domain architecture and family features reported in current literature (Trzaskalski 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Bat evolution and Desmodus context: Comparative analyses include Desmodus rotundus among bat species surveyed and demonstrate stronger, frequent positive selection at DPP4 residues contacting coronaviruses, implying potential adaptive divergence in the vampire bat ortholog while preserving core catalytic architecture (Frank 2022) (frank2022exceptionaldiversityand pages 2-2). A 2024 updated MERS review also discusses bat DPP4 orthologs, including reference to Desmodus rotundus DPP4 in the context of receptor usage (Novas 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 273-277).
- Limitation and inference: Direct functional or expression studies specific to K9J2R0 (vampire bat DPP4) remain limited in the accessible literature; functional annotation therefore relies on strong cross‑species conservation of catalytic motifs/domains and bat‑focused evolutionary context.

7) Functional annotation for K9J2R0 (Desmodus rotundus DPP4/CD26)
- Primary function: Membrane-anchored, dimeric serine exopeptidase that removes N‑terminal dipeptides from peptides with penultimate Pro or Ala; catalytic triad Ser–Asp–His and Glu205/Glu206 loop mediate recognition/catalysis; N710 and R125 contribute to substrate positioning and discrimination (Gnoth 2024; Trzaskalski 2024) (lin2026structuralbasisfor pages 1-2, trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Substrate scope and pathway roles: Likely processes incretins (GLP‑1, GIP) and chemokines (e.g., SDF‑1, RANTES, IP‑10), thereby modulating glucose homeostasis and immune cell trafficking; non‑catalytic interactions include ADA binding that modulates extracellular adenosine signaling impacting T‑cell activation (Trzaskalski 2024; Kotrulev 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Localization: Plasma membrane type II glycoprotein with extracellular ectodomain; also present as sDPP4 after shedding by MMPs/KLK5; glycosylation (Asn319) is required for correct surface delivery and activity (Trzaskalski 2024) (trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51).
- Coronavirus receptor: The DPP4 ectodomain serves as entry receptor for MERS‑CoV and several merbecoviruses in other mammals; structural data define binding on β‑propeller blades IV–V with species‑dependent interface geometry; the cytoplasmic tail is not required for entry, indicating ectodomain sufficiency and involvement of additional host factors (Yang 2024; Thankamani 2024) (yang2024structuralbasisfor pages 3-5). Pangolin/bat merbecoviruses display variable affinity to hDPP4, with determinants including RBD approach angle and contacts with hDPP4 glycan N321 (Yang 2024; Lin 2026) (yang2024structuralbasisfor pages 12-13, lin2026structuralbasisfor pages 1-2, yang2024structuralbasisfor pages 3-5). These insights, together with bat evolutionary selection on DPP4, support the inference that K9J2R0 retains the structural receptor interface characteristic of mammalian DPP4 (frank2022exceptionaldiversityand pages 2-2, yang2024structuralbasisfor pages 3-5).

References with URLs and dates
- Trzaskalski NA. Dipeptidyl peptidase‑4 in cardiometabolic disease. 2024. Key mechanistic, structural, and shedding details (trzaskalski2024dipeptidylpeptidase4ina pages 273-277, trzaskalski2024dipeptidylpeptidase4ina pages 47-51, trzaskalski2024dipeptidylpeptidase4in pages 47-51). URL not provided in excerpt; 2024.
- Gnoth K et al. Contribution of amino acids in the active site of dipeptidyl peptidase 4 to the catalytic action of the enzyme. PLOS ONE. Apr 24, 2024. https://doi.org/10.1371/journal.pone.0289239 (lin2026structuralbasisfor pages 1-2).
- Yang M et al. Structural basis for human DPP4 receptor recognition by a pangolin MERS‑like coronavirus. PLOS Pathogens. Nov 8, 2024. https://doi.org/10.1371/journal.ppat.1012695 (yang2024structuralbasisfor pages 12-13, yang2024structuralbasisfor pages 3-5).
- Thankamani K et al. MERS‑CoV internalization does not rely on DPP4 cytoplasmic tail signaling. npj Viruses. Dec 16, 2024. https://doi.org/10.1038/s44298-024-00080-y ().
- Frank HK et al. Exceptional diversity and selection pressure on coronavirus host receptors in bats compared to other mammals. Proc. R. Soc. B. Jul 6, 2022. https://doi.org/10.1098/rspb.2022.0193 (frank2022exceptionaldiversityand pages 2-2).
- Kotrulev M, Gomez-Touriño I, Cordero OJ. Soluble CD26: From suggested biomarker for cancer diagnosis to plausible marker for dynamic monitoring of immunotherapy. Cancers. Jun 22, 2024. https://doi.org/10.3390/cancers16132427 ().
- Suzuki Y et al. Transcriptome Analysis of Fibroblasts in Hypoxia-Induced Vascular Remodeling: Functional Roles of CD26/DPP4. Int J Mol Sci. Nov 29, 2024. https://doi.org/10.3390/ijms252312599 ().
- Lin Z et al. Structural basis for human DPP4 receptor recognition by MERS-like coronaviruses 2014‑422 and GX2012. PLOS Pathogens. Jan 7, 2026. https://doi.org/10.1371/journal.ppat.1013792 (lin2026structuralbasisfor pages 1-2).
- Novas IP. An updated review on MERS. 2024. Bat DPP4 (including Desmodus) discussion (trzaskalski2024dipeptidylpeptidase4ina pages 273-277). URL not provided in excerpt; 2024.

Notes and limitations
- Desmodus rotundus-specific functional studies for K9J2R0 were not found in the accessible texts; however, strong conservation of catalytic motifs/domains and convergent bat evolutionary pressures at coronavirus-contacting residues justify functional inference from mammalian DPP4 literature (frank2022exceptionaldiversityand pages 2-2). Further species-specific experiments (sequence comparison at catalytic and contact residues; enzymatic kinetics; binding assays with merbecovirus RBDs) are warranted to refine annotation for K9J2R0.

References

1. (trzaskalski2024dipeptidylpeptidase4ina pages 47-51): NA Trzaskalski. Dipeptidyl peptidase-4 in cardiometabolic disease. Unknown journal, 2024.

2. (trzaskalski2024dipeptidylpeptidase4in pages 47-51): NA Trzaskalski. Dipeptidyl peptidase-4 in cardiometabolic disease. Unknown journal, 2024.

3. (trzaskalski2024dipeptidylpeptidase4ina pages 273-277): NA Trzaskalski. Dipeptidyl peptidase-4 in cardiometabolic disease. Unknown journal, 2024.

4. (lin2026structuralbasisfor pages 1-2): Zichun Lin, Teng Gao, and Xinquan Wang. Structural basis for human dpp4 receptor recognition by mers-like coronaviruses 2014-422 and gx2012. PLOS Pathogens, 22:e1013792, Jan 2026. URL: https://doi.org/10.1371/journal.ppat.1013792, doi:10.1371/journal.ppat.1013792. This article has 0 citations and is from a highest quality peer-reviewed journal.

5. (yang2024structuralbasisfor pages 12-13): Mo Yang, Zehou Li, Jing Chen, Yang Li, Ran Xu, Meihua Wang, Ying Xu, Rong Chen, Weiwei Ji, Xiaoxia Li, Jiayu Wei, Zhengrong Zhou, Minjie Ren, Ke Ma, Jiayu Guan, Guoxiang Mo, Peng Zhou, Bo Shu, Jingjing Guo, Yuan Yuan, Zheng-Li Shi, and Shuijun Zhang. Structural basis for human dpp4 receptor recognition by a pangolin mers-like coronavirus. PLOS Pathogens, 20:e1012695, Nov 2024. URL: https://doi.org/10.1371/journal.ppat.1012695, doi:10.1371/journal.ppat.1012695. This article has 5 citations and is from a highest quality peer-reviewed journal.

6. (yang2024structuralbasisfor pages 3-5): Mo Yang, Zehou Li, Jing Chen, Yang Li, Ran Xu, Meihua Wang, Ying Xu, Rong Chen, Weiwei Ji, Xiaoxia Li, Jiayu Wei, Zhengrong Zhou, Minjie Ren, Ke Ma, Jiayu Guan, Guoxiang Mo, Peng Zhou, Bo Shu, Jingjing Guo, Yuan Yuan, Zheng-Li Shi, and Shuijun Zhang. Structural basis for human dpp4 receptor recognition by a pangolin mers-like coronavirus. PLOS Pathogens, 20:e1012695, Nov 2024. URL: https://doi.org/10.1371/journal.ppat.1012695, doi:10.1371/journal.ppat.1012695. This article has 5 citations and is from a highest quality peer-reviewed journal.

7. (frank2022exceptionaldiversityand pages 2-2): Hannah K. Frank, David Enard, and Scott D. Boyd. Exceptional diversity and selection pressure on coronavirus host receptors in bats compared to other mammals. Proceedings of the Royal Society B, Jul 2022. URL: https://doi.org/10.1098/rspb.2022.0193, doi:10.1098/rspb.2022.0193. This article has 18 citations.

Citations

1. lin2026structuralbasisfor pages 1-2
2. frank2022exceptionaldiversityand pages 2-2
3. yang2024structuralbasisfor pages 3-5
4. yang2024structuralbasisfor pages 12-13
5. https://doi.org/10.1371/journal.pone.0289239
6. https://doi.org/10.1371/journal.ppat.1012695
7. https://doi.org/10.1371/journal.ppat.1013792
8. https://doi.org/10.1038/s44298-024-00080-y
9. https://doi.org/10.3390/ijms252312599
10. https://doi.org/10.3390/cancers16132427
11. https://doi.org/10.1098/rspb.2022.0193
12. https://doi.org/10.1371/journal.ppat.1013792,
13. https://doi.org/10.1371/journal.ppat.1012695,
14. https://doi.org/10.1098/rspb.2022.0193,