1EM1

X-RAY CRYSTAL STRUCTURE FOR HUMAN MANGANESE SUPEROXIDE DISMUTASE, Q143A

Summary for 1EM1

• Entry DOI: 10.2210/pdb1em1/pdb
• Descriptor: MANGANESE SUPEROXIDE DISMUTASE, SULFATE ION, MANGANESE (II) ION, ... (4 entities in total)
• Functional Keywords: alpha-beta protein, metalloenzyme, oxidoreductase
• Biological source: Homo sapiens (human)
• Cellular location: Mitochondrion matrix: P04179
• Total number of polymer chains: 2
• Total formula weight: 44654.12

Authors

Leveque, V.,Stroupe, M.E.,Lepock, J.R.,Cabelli, D.E.,Tainer, J.A.,Nick, H.S.,Silverman, D.N. (deposition date: 2000-03-14, release date: 2000-03-24, Last modification date: 2024-02-07)

Primary citation

Leveque, V.J.,Stroupe, M.E.,Lepock, J.R.,Cabelli, D.E.,Tainer, J.A.,Nick, H.S.,Silverman, D.N.
Multiple replacements of glutamine 143 in human manganese superoxide dismutase: effects on structure, stability, and catalysis.
Biochemistry, 39:7131-7137, 2000

PubMed Abstract: 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.

PubMed: 10852710
DOI: 10.1021/bi9929958

Experimental method

X-RAY DIFFRACTION (2.13 Å)