D99 Type I Signal Peptidase Implicated Stabilizing the Protein Structure

Type I 신호펩디드 가수분해효소에 존재하는 D99 아미노산 잔기의 구조적 역할 가능성

  • Sung, Meesook (Department of Biochemistry, College of Medicine, Kwandong University) ;
  • Eunyoung Han (Department of Biochemistry, College of Medicine, Kwandong University) ;
  • Lee, Hoyoung (Department of Biochemistry, College of Medicine, Kwandong University)
  • Published : 2003.06.01


Type Ⅰ signal peptidase is an integral membrane protein that functions to cleave signal peptides from secreted and membrane proteins. The enzyme serves as a potential target for the development of novel antibacterial agents due to its unique physiological properties. Despite being one of the best characterized enzymes, the catalysis of Type Ⅰ signal peptidase still remains controversy over the catalytic serine/lysine dyad mechanism. It appears that the dyad proteases are generally less efficient than the prototypical serine/histidine/aspartic acid triad found in most enzymes, although Type Ⅰ signal peptidase is an exception to this rule. In this paper, we have proposed that Type Ⅰ signal peptidase may act as the serine/lysine/aspartic acid triad cataltytic mechanism. Therefore, the aspartic acid 99 residue in the E. coli signal peptidase was chosen and mutated to an alanine to see if there is any possible role of the aspartic acid in the catalytic function. Type Ⅰ signal peptidase D99A protein was inactive in vitro assay using the procoat synthesized by in vitro transcription translation. However, the mutant was active using a highly sensitive in vivo assay. Pulse-chase experiments show that the replacement of aspartic acid 99 with alanine results in a very unstable signal peptidase molecule. Therefore, we conclude that it is unlikely that the residue is directly involved in catalysis, but rather plays an important role in stabilizing the protein structure.


Signal peptidase;site-directed mutagenesis


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