1em1
From Proteopedia
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X-RAY CRYSTAL STRUCTURE FOR HUMAN MANGANESE SUPEROXIDE DISMUTASE, Q143A
Overview
Glutamine 143 in human manganese superoxide dismutase (MnSOD) forms a, hydrogen bond with the manganese-bound solvent molecule and is, investigated by replacement using site-specific mutagenesis. Crystal, structures showed that the replacement of Gln 143 with Ala made no, significant change in the overall structure of the mutant enzyme. Two new, water molecules in Q143A MnSOD were situated in positions nearly identical, with the Oepsilon1 and Nepsilon2 of the replaced Gln 143 side chain and, maintained a hydrogen-bonded network connecting the manganese-bound, solvent molecule to other residues in the active site. However, their, presence could not sustain the stability and activity of the enzyme; the, main unfolding transition of Q143A was decreased 16 degrees C and its, catalysis decreased 250-fold to k(cat)/K(m) = 3 x 10(6) M(-)(1) s(-)(1), as determined by stopped-flow spectrophotometry and pulse radiolysis. The, mutant Q143A MnSOD and other mutants at position 143 showed very low, levels of product inhibition and favored Mn(II)SOD in the resting state, whereas the wild type showed strong product inhibition and favored, Mn(III)SOD. However, these differences did not affect the rate constant, for dissociation of the product-inhibited complex in Q143A MnSOD which was, determined from a characteristic absorbance at 420 nm and was comparable, in magnitude ( approximately 100 s(-)(1)) to that of the wild-type enzyme., Hence, Gln 143, which is necessary for maximal activity in superoxide, dismutation, appears to have no role in stabilization and dissociation of, the product-inhibited complex.
About this Structure
1EM1 is a Single protein structure of sequence from Homo sapiens with SO4 and MN as ligands. Active as Superoxide dismutase, with EC number 1.15.1.1 Full crystallographic information is available from OCA.
Reference
Multiple replacements of glutamine 143 in human manganese superoxide dismutase: effects on structure, stability, and catalysis., Leveque VJ, Stroupe ME, Lepock JR, Cabelli DE, Tainer JA, Nick HS, Silverman DN, Biochemistry. 2000 Jun 20;39(24):7131-7. PMID:10852710
Page seeded by OCA on Mon Nov 12 16:44:47 2007
