Structural characterization of Salmonella typhimurium YeaZ, an M22 O‐sialoglycoprotein endopeptidase homolog

AbstractThe Salmonella typhimurium “yeaZ” gene (StyeaZ) encodes an essential protein of unknown function (StYeaZ), which has previously been annotated as a putative homolog of the Pasteurella haemolytica M22 O‐sialoglycoprotein endopeptidase Gcp. YeaZ has also recently been reported as the first example of an RPF from a gram‐negative bacterial species. To further characterize the properties of StYeaZ and the widely occurring MK‐M22 family, we describe the purification, biochemical analysis, crystallization, and structure determination of StYeaZ. The crystal structure of StYeaZ reveals a classic two‐lobed actin‐like fold with structural features consistent with nucleotide binding. However, microcalorimetry experiments indicated that StYeaZ neither binds polyphosphates nor a wide range of nucleotides. Additionally, biochemical assays show that YeaZ is not an active O‐sialoglycoprotein endopeptidase, consistent with the lack of the critical zinc binding motif. We present a detailed comparison of YeaZ with available structural homologs, the first reported structural analysis of an MK‐M22 family member. The analysis indicates that StYeaZ has an unusual orientation of the A and B lobes which may require substantial relative movement or interaction with a partner protein in order to bind ligands. Comparison of the fold of YeaZ with that of a known RPF domain from a gram‐positive species shows significant structural differences and therefore potentially distinctive RPF mechanisms for these two bacterial classes. Proteins 2006. © 2006 Wiley‐Liss, Inc.