| Protein/form | Approx. MW / cleavage | Domain architecture | Enzymatic activity | Structural role / localization | Key evidence | Year | DOI / URL |
|---|---|---|---|---|---|---|---|
| Precursor gp5 (gene 5 product; UniProt P16009) | Synthesized as ~63 kDa precursor; maturational cleavage occurs between Ser351 and Ala352 during baseplate assembly or at high concentration (pqac-00000001, pqac-00000012) | N-terminal OB-fold/antiparallel β-barrel, central lysozyme-like muramidase domain, and C-terminal β-helix-forming region that yields the needle/prism after cleavage (pqac-00000012, pqac-00000014) | EC 3.2.1.17 N-acetylmuramidase; cleaves the β-1,4 glycosidic bond between NAM and NAG in peptidoglycan; substrate specificity similar to T4 gpE lysozyme (pqac-00000000, pqac-00000005) | Virion/baseplate-associated precursor of the central cell-puncturing device; required for proper hub/baseplate assembly and infectivity (pqac-00000012, pqac-00000003) | Produced as precursor then processed during assembly; gene 5 mutants lack proper hub and are noninfectious; Leprince 2023 places gp5 in the T4 central puncturing apparatus with gp27 and gp5.4 (pqac-00000001, pqac-00000012, pqac-00000003) | 2002; 2004; 2023 | Nature 10.1038/415553a https://doi.org/10.1038/415553a; Mol Microbiol 10.1046/j.1365-2958.2003.03894.x https://doi.org/10.1046/j.1365-2958.2003.03894.x; Viruses 10.3390/v15010196 https://doi.org/10.3390/v15010196 |
| Processed gp5* (mature N-terminal portion retained in complex) | Mature form ~43 kDa; also observed near ~40 kDa on zymogram/SDS-PAGE; generated from precursor during assembly; cleavage at Ser351-Ala352 (pqac-00000001, pqac-00000006, pqac-00000012) | Contains N-terminal OB-fold plus peripheral lysozyme domain; associates with gp27 and gp5C in assembled heterononamer (gp27-gp5*-gp5C)3 (pqac-00000013, pqac-00000014) | N-acetylmuramidase with reduced activity in trimeric assembled state; removal of the C-terminal fragment increases activity about 10-fold (pqac-00000001, pqac-00000014) | Part of the gp27-gp5 central spike or hub beneath the baseplate; lysozyme domains surround the β-helix and act during localized peptidoglycan digestion for tail-tube penetration (pqac-00000011, pqac-00000013) | Virion-associated muralytic band at ~40 kDa; mature baseplate protein proposed to digest cell wall during infection and implicated in lysis from without or within phenotypes (pqac-00000000, pqac-00000006, pqac-00000011) | 2002; 2004 | Nature 10.1038/415553a https://doi.org/10.1038/415553a; Mol Microbiol 10.1046/j.1365-2958.2003.03894.x https://doi.org/10.1046/j.1365-2958.2003.03894.x |
| gp5C (C-terminal cleavage product) | C-terminal product from cleavage of gp5 precursor; forms SDS-resistant trimer; exact mass not separately emphasized in the cited summaries (pqac-00000013) | Triple-stranded or three-start β-helix forming a pointed triangular prism or needle, about 110 Å long and 28 Å in diameter; includes repeated VXGXXXXX motifs (pqac-00000013, pqac-00000014) | No catalytic muramidase activity assigned; primarily structural, but modulates gp5* activity by stabilizing the trimeric state (pqac-00000013, pqac-00000014) | Membrane-puncturing needle of the central cell-puncturing device; with gp27 forms a torch-like hub at the baseplate center that is driven toward the host envelope during sheath contraction (pqac-00000011, pqac-00000013) | Crystal structure shows gp5C is required for trimerization of the gp27-gp5 complex and for formation of the rigid puncturing prism or needle (pqac-00000013, pqac-00000014) | 2002 | Nature 10.1038/415553a https://doi.org/10.1038/415553a |
| gp27-gp5 central device (assembled functional complex) | Heterononameric (gp27-gp5*-gp5C)3 complex; overall torch-like assembly about 190 Å long; gp27 cylinder about 60 Å long; β-helix spans the needle region (pqac-00000013, pqac-00000011) | gp27 trimer forms hollow cylinder or head; gp5 contributes OB-fold, lysozyme domains, and C-terminal β-helix needle; Leprince 2023 summarizes a lysozyme domain plus β-rich puncturing region (pqac-00000013, pqac-00000003) | Couples mechanical puncture with localized peptidoglycan hydrolysis to enable DNA injection through the cell envelope (pqac-00000011, pqac-00000003) | Central hub of the T4 baseplate and cell-puncturing apparatus; located at the distal tail tip and aligned with the tail tube for host membrane and peptidoglycan penetration during adsorption and sheath contraction (pqac-00000012, pqac-00000003) | Structural model from Kanamaru 2002 plus biochemical support from Moak and Molineux 2004; Leprince 2023 places this device in the current adsorption and penetration framework (pqac-00000012, pqac-00000005, pqac-00000003) | 2002; 2004; 2023 | Nature 10.1038/415553a https://doi.org/10.1038/415553a; Mol Microbiol 10.1046/j.1365-2958.2003.03894.x https://doi.org/10.1046/j.1365-2958.2003.03894.x; Viruses 10.3390/v15010196 https://doi.org/10.3390/v15010196 |


*Table: This table summarizes the validated identity, processing, domain structure, enzymatic activity, and structural role of Enterobacteria phage T4 gene 5 product gp5 (UniProt P16009). It highlights the core evidence from Kanamaru 2002, Moak and Molineux 2004, and Leprince 2023 most useful for functional annotation.*