NCGR_LOCUS27674 (A0A811PC48) Review Notes

Gene Identity

• UniProt: A0A811PC48 (TrEMBL, unreviewed)
• Organism: Miscanthus lutarioriparius (NCBITaxon:422564), a C4 grass in order Poales
• Annotated as: UMP-CMP kinase (EC 2.7.4.14)
• Length: 714 amino acids / 78.8 kDa
• Evidence level: PE3 (Inferred from homology)
• Source: Whole genome shotgun sequence [EMBL:CAD6242091.1]

Key Concern: Likely Chimeric Gene Model

This protein is almost certainly a chimeric gene model artifact resulting from incorrect fusion of two separate genes during genome annotation:

Evidence for chimeric model:

1. Abnormal size: 714 AA is 2-3.5x larger than any known UMP-CMP kinase:
2. Arabidopsis UMP-CMP kinase: 202 AA PMID:9736767
3. Rice YL2 (chloroplastic UMK): 351 AA including transit peptide PMID:29866037
4. Human CMPK1: 196-228 AA

5. E. coli CMP kinase: 225 AA

6. Two unrelated domains:

7. N-terminal: Adenylate kinase domain (Pfam PF00406, ADK) - consistent with UMP-CMP kinase

8. C-terminal (positions 555-650): Chalcone isomerase domain (Pfam PF16035, Chalcone_2) - functionally unrelated

9. Conflicting automated annotations from different domains:

10. UMP/CMP/dCMP kinase activities (from ADK domain via HAMAP/UniRule)
11. Fatty acid binding (from CHI-fold domain via PANTHER/TreeGrafter)

12. Intramolecular lyase activity (from CHI-fold superfamily via InterPro)

13. Genome annotation context: The M. lutarioriparius genome has 68,328 predicted gene models PMID:33931638, which is very high even for an allotetraploid grass. The EVidenceModeler pipeline used is known to sometimes produce chimeric models in polyploid genomes.

The two likely constituent genes:

Gene 1 (N-terminal ~350 AA): A plastid/chloroplast-targeted UMP-CMP kinase
- Consistent with rice YL2 ortholog PMID:29866037 or Arabidopsis PUMPKIN PMID:30523175
- Plant plastid UMKs have transit peptides and are 300-350 AA total
- Functions in de novo pyrimidine nucleotide biosynthesis in chloroplasts

Gene 2 (C-terminal ~150+ AA): A CHI-fold fatty acid-binding protein (FAP)
- The Chalcone_2 domain (PF16035) belongs to the CHI superfamily
- FAP subfamily members are non-catalytic - they bind fatty acids but lack isomerase activity PMID:22388820
- Plant FAPs typically localize to plastids for de novo fatty acid biosynthesis PMID:22388820

Annotation Assessment

All 13 GO annotations are IEA (electronic). Given the chimeric nature:

Annotations likely correct for the UMP-CMP kinase portion:

• GO:0033862 UMP kinase activity (UniRule)
• GO:0036430 dCMP kinase activity (UniRule)
• GO:0036431 CMP kinase activity (UniRule)
• GO:0005524 ATP binding (InterPro)
• GO:0019205 nucleobase-containing compound kinase activity (InterPro)
• GO:0016776 phosphotransferase activity, phosphate group as acceptor (InterPro)
• GO:0006221 pyrimidine nucleotide biosynthetic process (UniProt)
• GO:0006207 'de novo' pyrimidine nucleobase biosynthetic process (InterPro)

Annotations likely from the CHI-fold/FAP portion (erroneous for whole protein):

• GO:0005504 fatty acid binding (TreeGrafter/PANTHER) - from FAP domain
• GO:0016872 intramolecular lyase activity (InterPro) - from CHI superfamily, but FAPs are non-catalytic

Localization annotations:

• GO:0005737 cytoplasm - plausible for UMK
• GO:0005634 nucleus - plausible for UMK (some UMKs are nuclear)
• GO:0009570 chloroplast stroma - plausible if this is a plastid-targeted UMK, though rice YL2 localizes to thylakoid membranes, not stroma

References

• PMID:9736767 - Arabidopsis UMP-CMP kinase characterization
• PMID:29866037 - Rice YL2 chloroplastic UMP kinase
• PMID:30523175 - Arabidopsis PUMPKIN plastid UMP kinase
• PMID:22388820 - CHI-fold FAP proteins and fatty acid binding
• PMID:33931638 - Miscanthus lutarioriparius genome assembly