This family includes baseplate wedge protein gp6 (gp6) from bacteriophage T4 and its relatives. Contractile tail bacteriophages use a multiprotein tubular apparatus resembling a coiled spring wound round a rigid tube to attach to and penetrate host cell membranes. The structure known as the baseplate replays the contraction signal to the sheath [, ]. gp6 is located next to the tail tube and is an intermediate (or inner) baseplate protein involved in tail assembly [, ]. Two molecules of gp6 form a complex with gp25 and gp7 which is involved sheath contraction [].
Gp6, a Staphylococcus aureus pathogenicity island 1 protein, is a mobile genetic element that carries genes for several superantigen toxins. It is a dimeric protein produced from the pathogenicity island with a helix-loop-helix motif similar to that of bacteriophage scaffolding proteins. It is thought to determine the size of the capsids of distribution of the SAPI1 genome as it acts as an internal scaffolding protein during capsid size determination [].
The bacteriophage portal protein forms a gateway, or portal, enabling DNA passage during packaging and ejection of the phage genome. It also forms the junction between the phage head (capsid) and the tail proteins []. During SPP1 morphogenesis, Gp6 participates in the procapsid assembly reaction [, ].In the mature SPP1 virion, the portal protein, GP6, exists as a dodecamer, whereas recombinant SPP1 Gp6 has been shown to form 13-subunit assemblies [, ].This entry includes Bacillus phage SPP1-type portal proteins, Mycobacterium phage portal proteins and putative portal proteins of the Listeria phage A118-type.
This family of proteins contain head-tail connector proteins related to gp6 from bacteriophage HK97 []. The gp15 protein of Bacillus phage SPP1, for which the tertiary structure is known, is included in this entry [].This family contain head-tail connector proteins related to gp6 from bacteriophage HK97 [], including the head completion protein from Enterobacteria phage T5 (also known as T5p144) that closes the capsid once the viral DNA has been packaged. These proteins show similarities to the gp6 protein of phage HK97, and, probably, it is part of the head-tail connector by binding to the portal protein and to the tail completion protein []. The bacteriophage HK97 gp6 protein is critical in the assembly of the connector, a specialized structure that serves as an interface for head and tail attachment, as well as a point at which DNA exits the head during infection by the bacteriophage []. The gp15 protein of Bacillus phage SPP1, for which the tertiary structure is known, is included in this entry [].
Members of this superfamily of viral baseplate structural proteins adopt a structure consisting of a three-layer β-sandwich with two finger-like loops containing an α-helix at the opposite sides of the sandwich. The two peripheral, five-stranded, antiparallel β-sheets are stacked against the middle, four-stranded, antiparallel β-sheet. Attachment of this family of proteins to the baseplate during assembly creates a binding site for subsequent attachment of Gp6 [].
Members of this family of viral baseplate structural proteins adopt a structure consisting of a three-layer β-sandwich with two finger-like loops containing an α-helix at the opposite sides of the sandwich. The two peripheral, five-stranded, antiparallel β-sheets are stacked against the middle, four-stranded, antiparallel β-sheet. Attachment of this family of proteins to the baseplate during assembly creates a binding site for subsequent attachment of Gp6 [].
This domain is found in baseplate protein Gp25 from phage T4 and related phages, and Gp25-like proteins from bacteria [, ]. Gp25 is a component of the conserved wedge in the inner part of the baseplate and serves as a nucleus for sheath polymerisation, playing a critical role in sheath assembly and contraction [, ]. The EPR motif (Glu-Pro-Arg, residues 85-87 of gp25) is conserved across all members of the family including orthologs from the RpoS-mediated general stress response system (called IraD) []. This motif interacts with the 'core bundle' composed of orthologs of T4 gp6 and gp7 proteins in contractile injection systems.
This family includes baseplate wedge protein gp7 (gp7) from bacteriophage T4 and its relatives. Contractile tail bacteriophages use a multiprotein tubular apparatus resembling a coiled spring wound round a rigid tube to attach to and penetrate host cell membranes. The structure known as the baseplate replays the contraction signal to the sheath [, ]. gp7 is an intermediate (or inner) baseplate protein involved in tail assembly []. It also forms a complex with gp25 and two molecules of gp6 which is involved in sheath contraction [].
This entry describes the head-tail adaptor protein of bacteriophage SPP1and related proteins in other bacteriophage and prophage regions of bacterial genomes. Homologues are also found in Gene Transfer Agents (GTA) [], including ORFg7 (RCAP_rcc01689) of the GTA of Rhodobacter capsulatus (Rhodopseudomonas capsulata) [].In bacteriophage SPP1, the gp16 protein functions as a stopper, locking the viral DNA into the capsid. When the tail attachment binds to the entry receptor, gp16 opens by a diaphragm-like motion, allowing the genome to exit the capsid through the tail tube to the host cell. During virion assembly, gp16 functions as a docking platform to which the preassembled tail binds [].The SPP1 head-to-tail connector is composed of cyclical dodecamers of the portal protein gp6 and of the 2 head completion proteins gp15 and gp16 [].
This entry describes the head-tail adaptor protein of bacteriophage SPP1and related proteins in other bacteriophage and prophage regions of bacterial genomes. Homologues are also found in Gene Transfer Agents (GTA) [], including ORFg7 (RCAP_rcc01689) of the GTA of Rhodobacter capsulatus (Rhodopseudomonas capsulata) [].In bacteriophage SPP1, the gp16 protein functions as a stopper, locking the viral DNA into the capsid. When the tail attachment binds to the entry receptor, gp16 opens by a diaphragm-like motion, allowing the genome to exit the capsid through the tail tube to the host cell. During virion assembly, gp16 functions as a docking platform to which the preassembled tail binds [].The SPP1 head-to-tail connector is composed of cyclical dodecamers of the portal protein gp6 and of the 2 head completion proteins gp15 and gp16 [].
