Crystal structure of a novel germination protease from spores of Bacillus megaterium: Structural arrangement and zymogen activation

The DNA in the core of spores of Bacillus species is saturated with a group of small, acid-soluble proteins (SASP) that protect DNA from a variety of harsh treatments and play a major role in spore resistance and long-term sp ore survival. During spore germination, SASPs are rapidly degraded to amino acids and this degradation is initiated by a sequence-specific protease ca lled germination protease (GPR), which exhibits no obvious mechanistic or a mino acid sequence similarity to any known class of proteases. GPR is synth esized during sporulation as an inactive tetrameric zymogen termed P-46, wh ich later autoprocesses to a smaller form termed P-41, which is active only during spore germination. Here, we report the crystal structure of P-46 fr om Bacillus megaterium at 3.0 Angstrom resolution and the fact that P46 mon omer adopts a novel fold. The asymmetric unit contains two P-46 monomers an d the functional tetramer is a dimer of dimers, with an similar to 9 Angstr om channel in the center of the tetramer. Analysis of the P-46 structure an d site-directed mutagenesis studies have provided some insight into the mec hanism of zymogen activation as well as the zymogen's lack of activity and the inactivity of P-41 in the mature spore. (C) 2000 Academic Press.