title: Biochemical characterization of signal peptidase I from gram-positive Streptococcus pneumoniae.
abstract: Bacterial signal peptidase I is responsible for proteolytic processing of the precursors of secreted proteins. The enzymes from gram-negative and -positive bacteria are different in structure and specificity. In this study, we have cloned, expressed, and purified the signal peptidase I of gram-positive Streptococcus pneumoniae. The precursor of streptokinase, an extracellular protein produced in pathogenic streptococci, was identified as a substrate of S. pneumoniae signal peptidase I. Phospholipids were found to stimulate the enzymatic activity. Mutagenetic analysis demonstrated that residues serine 38 and lysine 76 of S. pneumoniae signal peptidase I are critical for enzyme activity and involved in the active site to form a serine-lysine catalytic dyad, which is similar to LexA-like proteases and Escherichia coli signal peptidase I. Similar to LexA-like proteases, S. pneumoniae signal peptidase I catalyzes an intermolecular self-cleavage in vitro, and an internal cleavage site has been identified between glycine 36 and histidine 37. Sequence analysis revealed that the signal peptidase I and LexA-like proteases show sequence homology around the active sites and some common properties around the self-cleavage sites. All these data suggest that signal peptidase I and LexA-like proteases are closely related and belong to a novel class of serine proteases.
authors.affiliation: Infectious Diseases Research, Lilly Research Laboratories, Indianapolis, Indiana 46285, USA. Peng_Sheng-Bin@lilly.com
authors.forename: S B
authors.initials: SB
authors.lastname: Peng
authors.forename: L
authors.initials: L
authors.lastname: Wang
authors.forename: J
authors.initials: J
authors.lastname: Moomaw
authors.forename: R B
authors.initials: RB
authors.lastname: Peery
authors.forename: P M
authors.initials: PM
authors.lastname: Sun
authors.forename: R B
authors.initials: RB
authors.lastname: Johnson
authors.forename: J
authors.initials: J
authors.lastname: Lu
authors.forename: P
authors.initials: P
authors.lastname: Treadway
authors.forename: P L
authors.initials: PL
authors.lastname: Skatrud
authors.forename: Q M
authors.initials: QM
authors.lastname: Wang
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D006090:Gram-Negative Bacteria / Q000201:enzymology; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000494:pharmacology; D011498:Protein Precursors; D011499:Protein Processing, Post-Translational; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000187:drug effects / Q000378:metabolism*; D013296:Streptococcus pneumoniae / Q000201:enzymology*; D013297:Streptococcus pyogenes / Q000201:enzymology; D013300:Streptokinase / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D008565:Membrane Proteins; D010743:Phospholipids; D011498:Protein Precursors; D013300:Streptokinase; D012697:Serine Endopeptidases; C026515:type I signal peptidase