Electrostatic role of aromatic ring stacking in the pH-sensitive modulation of a chymotrypsin-type serine protease, Achromobacter protease I.
Achromobacter protease I (API) has a unique region of aromatic ring stacking with Trp169-His210 in close proximity to the catalytic triad. This paper reveals the electrostatic role of aromatic stacking in the shift in optimum pH to the alkaline region, which is the highest pH range (8.5-10) among chymotrypsin-type serine proteases. The pH-activity profile of API showed a sigmoidal distribution that appears at pH 8-10, with a shoulder at pH 6-8. Variants with smaller amino acid residues substituted for Trp169 had lower pH optima on the acidic side by 0-0.9 units. On the other hand, replacement of His210 by Ala or Ser lowered the acidic rim by 1.9 pH units, which is essentially identical to that of chymotrypsin and trypsin. Energy minimization for the mutant structures suggested that the side-chain of Trp169 stacked with His210 was responsible for isolation of the electrostatic interaction between His210 and the catalytic Asp113 from solvent. The aromatic stacking regulates the low activity at neutral pH and the high activity at alkaline pH due to the interference of the hydrogen bonded network in the catalytic triad residues.
Shiraki
Kentaro
K
School of Materials Science, Japan Advanced Institute of Science and Technology, Ishikawa, Japan. kshiraki@jaist.ac.jp
Norioka
Shigemi
S
Li
Shaoliang
S
Yokota
Kiyonobu
K
Sakiyama
Fumio
F
D000421:Alcaligenes / Q000201:enzymology*; D019943:Amino Acid Substitution; D000818:Animals; D001224:Aspartic Acid / Q000737:chemistry; D020134:Catalytic Domain; D002417:Cattle; D002918:Chymotrypsin / Q000737:chemistry; D006639:Histidine / Q000737:chemistry; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D009994:Osmolar Concentration; D012697:Serine Endopeptidases / Q000737:chemistry*; D012997:Solvents; D013045:Species Specificity; D055672:Static Electricity; D014357:Trypsin / Q000737:chemistry; D014364:Tryptophan / Q000737:chemistry
D012997:Solvents; D001224:Aspartic Acid; D006639:Histidine; D014364:Tryptophan; D012697:Serine Endopeptidases; D002918:Chymotrypsin; D014357:Trypsin; C036813:lysyl endopeptidase