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Microvirus H protein (pilot protein) A single molecule of H protein is found on each of the 12 spikes on the microvirus shell. H is involved in the ejection of the phage DNA, and at least one copy is injected into the host's periplasmic space along with the ssDNA viral genome. Part of H is thought to lie outside the shell, where it recognizes lipopolysaccharide from virus-sensitive strains. Part of H may lie within the capsid, since mutations in H can influence the DNA ejection mechanism by affecting the DNA-protein interactions. H may span the capsid through the hydrophilic channels formed by G proteins. Elucidation of the DNA-ejection mechanism from the crystal structure of part of the H protein shows that this tail-less icosahedral, single-stranded DNA phiX174-like coliphage bacteriophage requires H as a pilot protein for its DNA-delivery. H oligomerises to form a tube the function of which seems to be the delivery of the DNA genome across the host's periplasmic space into the host cytoplasm. The tube is constructed of ten alpha-helices with their amino termini arrayed in a right-handed super-helical coiled-coil and their carboxy termini arrayed in a left-handed super-helical coiled-coil. The tube spans the periplasmic space and is present while the genome is being delivered into the host cell's cytoplasm. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",