1pm9

Publication Abstract from PubMed

The side chains of His30 and Tyr166 from adjacent subunits in the homotetramer human manganese superoxide dismutase (Mn-SOD) form a hydrogen bond across the dimer interface and participate in a hydrogen-bonded network that extends to the active site. Compared with wild-type Mn-SOD, the site-specific mutants H30N, Y166F, and the corresponding double mutant showed 10-fold decreases in steady-state constants for catalysis measured by pulse radiolysis. The observation of no additional effect upon the second mutation is an example of cooperatively interacting residues. A similar effect was observed in the thermal stability of these enzymes; the double mutant did not reduce the major unfolding transition to an extent greater than either single mutant. The crystal structures of these site-specific mutants each have unique conformational changes, but each has lost the hydrogen bond across the dimer interface, which results in a decrease in catalysis. These same mutations caused an enhancement of the dissociation of the product-inhibited complex. That is, His30 and Tyr166 in wild-type Mn-SOD act to prolong the lifetime of the inhibited complex. This would have a selective advantage in blocking a cellular overproduction of toxic H2O2.

Amino acid substitution at the dimeric interface of human manganese superoxide dismutase.,Hearn AS, Fan L, Lepock JR, Luba JP, Greenleaf WB, Cabelli DE, Tainer JA, Nick HS, Silverman DN J Biol Chem. 2004 Feb 13;279(7):5861-6. Epub 2003 Nov 24. PMID:14638684^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.