Crystal structure of prolyl aminopeptidase from Serratia marcescens

Prolyl aminopeptidase from Serratia marcescens specifically catalyzes the r emoval of N-terminal proline residues from peptides, We have solved its thr ee-dimensional structure at 2.3 Angstrom resolution by the multiple isomorp hous replacement method. The enzyme consists of two contiguous domains. The larger domain shows the general topology of the alpha/beta hydrolase fold, with a central eight-stranded beta-sheet and six helices, The smaller doma in consists of six helices, The catalytic triad (Ser113, His296, and Asp268 ) is located near the large cavity at the interface between the two domains . Cys271, which is sensitive to SH reagents, is located near the catalytic residues, in spite of the fact that the enzyme is a serine peptidase, The s pecific residues which make up the hydrophobic pocket line the smaller doma in, and the specificity of the exo-type enzyme originates from this smaller domain. which blocks the N-terminal of P1 proline.