Analysis of near-neighbor contacts in bacteriophage T4 wedges and hubless baseplates by using a cleavable chemical cross-linker.

Abstract

Although bacteriophage T4 baseplate morphogenesis has been analyzed in some detail, there is little information available on the spatial arrangement and associations of its 150 subunits. We have therefore carried out the first analysis of its near-neighbor interactions by using the cleavable chemical cross-linker ethylene glycolbis(succinimidylsuccinate). In this report, we describe the cross-linked complexes that have been identified in the one-sixth arms or wedges and also in baseplatelike structures called rings consisting of six wedges but lacking the central hub, both of which are purified from T4 gene 5- -infected cells. Thirty different complexes were identified, of which about half contain multimers of a single species and half contain two different species. In general, the complexes reflect and support the assembly pathway derived by Kikuchi and King (Y. Kikuchi and J. King, J. Mol. Biol. 99:695-716, 1975) but broaden its scope to include such complexes as gp25-gp53, gp25-gp48, and gp48-gp53, which locate the gp48 binding site over the inner edge of the ring but outside the central hub. The data also supports the view that wedges are assembled from the outer edge inward toward the central hub. Wedge-wedge contact in rings was mediated primarily by gp12 and gp9, the absence of which dramatically destabilized the ring----wedge equilibrium in favor of wedges. Although no heterologous complexes containing gp9 were identified, gp12 contacts unique to rings were observed with both gp10 and gp11.