FORMATION OF A NOVEL 4-HELIX BUNDLE AND MOLECULAR RECOGNITION SITES BY DIMERIZATION OF A RESPONSE REGULATOR PHOSPHOTRANSFERASE

A basis for understanding specificity of molecular recognition between phosphorelay proteins has been deduced from the 2.6 Angstrom structur e of the Spo0B phosphotransferase of the phosphorelay regulating sporu lation initiation. Spo0B consists of two domains: an M-terminal alpha- helical hairpin domain and a C-terminal alpha/beta domain. Two subunit s of Spo0B dimerize by a parallel association of helical hairpins to f orm a novel four-helix bundle from which the active histidine protrude s. Docking studies show that both the monomers interact with a Spo0F m olecule at the region surrounding the active site aspartate to positio n it for phosphotransfer. It is apparent that different surfaces of re sponse regulators may be involved in recognition of the protein partne rs to which they are paired.