Biochemical characterization of signal peptidase I from gram-positive Streptococcus pneumoniae.
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.
Peng
S B
SB
Infectious Diseases Research, Lilly Research Laboratories, Indianapolis, Indiana 46285, USA. Peng_Sheng-Bin@lilly.com
Wang
L
L
Moomaw
J
J
Peery
R B
RB
Sun
P M
PM
Johnson
R B
RB
Lu
J
J
Treadway
P
P
Skatrud
P L
PL
Wang
Q M
QM
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
D008565:Membrane Proteins; D010743:Phospholipids; D011498:Protein Precursors; D013300:Streptokinase; D012697:Serine Endopeptidases; C026515:type I signal peptidase