W0134

The phosphorelay and signal trasduction in sporulation: Crystal Structures of Spo0F and Spo0B from Bacillus subtilis. K. I. Varughese, Madhusudan, Xiao Zhen Zhou, John Whiteley and James Hoch, The Department of Molecular and Experimental Medicine, NX-1, The Scripps Research Institute, La Jolla, CA-92037 USA

Cells possess many sensors or receptors for chemical and protein stimuli that require signal transmission to other proteins to carry out an action to respond to the stimulating signal. Phosphoryl group transfer from one protein to another is the basis for propagating information in phosphorylation activated signal transduction. Bacteria and many eukaryotes (e.g., yeast, fungi and plants) have adapted the phosphorylation-dependent two-component paradigm to couple signal recognition, signal transduction and signal response. The basic units of two-component systems are a histidine kinase and a response regulator. The sporulation pathway in B. subtilis makes use of an expanded version of the two component system with 4 main components Kin-A, Spo0F, Spo0B and Spo0A. We had earlier determined the crystal structure of the secondary messenger Spo0F and now the structure of Spo0B the phosphotransferase at 2.6 ( resolution. Spo0B transfers a phosphoryl moiety from an aspartic residue in Spo0F to an aspartic residue in Spo0A by undergoing transient phosphorylation on a histidine residue. The structure of Spo0B consists of two domains- an N-terminal (-helical hairpin and a C-terminal (/( domain. The hairpins from two monomers associate in a parallel manner to form a novel type of four helix bundle at the interface of the dimer. The residue that undergoes phosphorylation, His30, is located in the middle of a helix in the four helical bundle and it is solvent exposed. The active site is formed by residues from both monomers. Docking studies show that Spo0F can fit into the active site bringing Asp-P in close proximity to His30 for phosphate transfer.