PMID- 8485129
OWN - NLM
STAT- MEDLINE
DCOM- 19930604
LR  - 20190613
IS  - 0006-2960 (Print)
IS  - 0006-2960 (Linking)
VI  - 32
IP  - 17
DP  - 1993 May 4
TI  - Structural consequences of hydrophilic amino acid substitutions in the 
      hydrophobic pocket of human carbonic anhydrase II.
PG  - 4506-14
AB  - The three-dimensional structures of Leu-198-->Glu, Leu-198-->His, Leu-198-->Arg, 
      and Leu-198-->Ala variants of human carbonic anhydrase II (CAII) have each been 
      determined by X-ray crystallographic methods to a resolution of 2.0 A. The side 
      chain of Leu-198 is located at the mouth of the active site hydrophobic pocket, 
      and this pocket is required for substrate association. Hydrophobic-->hydrophilic 
      amino acid substitutions at the mouth of the pocket decrease kcat/KM for CO2 
      hydration: the CO2 hydrase activities of Leu-198-->Glu, Leu-198-->His, and 
      Leu-198-->Arg CAIIs are diminished 19-fold, 10-fold, and 17-fold, respectively, 
      relative to the wild-type enzyme; however, the substitution of a compact 
      aliphatic side chain for Leu-198 has a smaller effect on catalysis, in that 
      Leu-198-->Ala CAII exhibits only a 3-fold decrease in CO2 hydrase activity 
      [Krebs, J. F., Rana, F., Dluhy, R. A., & Fierke, C. A. (1993) Biochemistry 
      (preceding paper in this issue)]. It is intriguing that CO2 hydrase activity is 
      not severely diminished in Leu-198-->Arg CAII, even though the side chain of 
      Arg-198 blocks the hydrophobic pocket. Therefore, the bulky side chain of Arg-198 
      must be reasonably mobile in order to accommodate substrate association. 
      Significantly, a residue larger than the wild-type Leu-198 side chain does not 
      necessarily block the substrate association pocket; e.g., the side chain of 
      Glu-198 packs against a hydrophobic patch, the net result of which is a wider 
      mouth for the pocket.(ABSTRACT TRUNCATED AT 250 WORDS)
FAU - Nair, S K
AU  - Nair SK
AD  - Department of Chemistry, University of Pennsylvania, Philadelphia 19104-6323.
FAU - Christianson, D W
AU  - Christianson DW
LA  - eng
GR  - GM07229/GM/NIGMS NIH HHS/United States
GR  - GM45614/GM/NIGMS NIH HHS/United States
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PT  - Research Support, U.S. Gov't, P.H.S.
PL  - United States
TA  - Biochemistry
JT  - Biochemistry
JID - 0370623
RN  - 0 (Amino Acids)
RN  - 0 (Guanidines)
RN  - EC 4.2.1.1 (Carbonic Anhydrases)
RN  - J41CSQ7QDS (Zinc)
RN  - JU58VJ6Y3B (Guanidine)
SB  - IM
MH  - Amino Acids/*chemistry
MH  - Binding Sites
MH  - Carbonic Anhydrases/*chemistry/metabolism
MH  - Crystallization
MH  - Electrochemistry
MH  - Guanidine
MH  - Guanidines/chemistry
MH  - Humans
MH  - Hydrogen Bonding
MH  - Hydrogen-Ion Concentration
MH  - Molecular Structure
MH  - Protein Conformation
MH  - X-Ray Diffraction
MH  - Zinc/metabolism
EDAT- 1993/05/04 00:00
MHDA- 1993/05/04 00:01
CRDT- 1993/05/04 00:00
PHST- 1993/05/04 00:00 [pubmed]
PHST- 1993/05/04 00:01 [medline]
PHST- 1993/05/04 00:00 [entrez]
AID - 10.1021/bi00068a005 [doi]
PST - ppublish
SO  - Biochemistry. 1993 May 4;32(17):4506-14. doi: 10.1021/bi00068a005.