Follow the protons: a low-barrier hydrogen bond unifies the mechanisms of the aspartic proteases.
Seven proton transfers in five steps participate in a catalytic turnover of an aspartic protease. The Rosetta Stone for elucidating their role is a low-barrier hydrogen bond that holds the two aspartic carboxyls in a coplanar conformation. The proton of this bond shuttles between oxygens during chemical steps via hydrogen tunneling, unlike in previous proposals where it was transferred to substrate. After the release of products, both carboxyls are protonated and the bond is missing. Re-forming the bond is a significant step within a kinetic isomechanism. The bond also explains-at long last-the extremely low pK in pH profiles.
Northrop
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DB
Division of Pharmaceutical Sciences, School of Pharmacy, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA. dbnorthrop@pharmacy.wisc.edu
D016282:Aspartic Acid Endopeptidases / Q000737:chemistry*; D002384:Catalysis; D025461:Feedback, Physiological; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D011522:Protons; D012997:Solvents / Q000737:chemistry
D011522:Protons; D012997:Solvents; D016282:Aspartic Acid Endopeptidases