Functional role of leucine-103 in myohemerythrin

Gregory M. Raner, Laura J. Martins, Walther R. Ellis

Research output: Contribution to journalArticle

19 Scopus citations

Abstract

Hemerythrins (Hrs) and myohemerythrins (Mhrs) are nonheme iron proteins that function as O2 carriers in four marine invertebrate phyla. Available amino acid sequences and X-ray structures indicate that a conserved leucine, residue 103 in the Themiste zostericola Mhr sequence, occupies a site distal to the Fe-O-Fe center. The side-chain methyl groups of the analogous leucine in Themiste dyscrita oxyHr are in van der Waals contact with bound O2 in the X-ray crystal structure, and this residue may therefore play a role in stabilizing bound dioxygen with respect to autoxidation. In order to test this hypothesis, the gene for T. zostericola Mhr was synthesized and expressed in Escherichia coli. Two mutant Mhrs, L103V and L103N, were also prepared. Optical spectra and kinetics data for these three proteins are presented. Importantly, neither mutant forms a stable oxy adduct; instead, rapid autoxidation results in formation of the corresponding met forms. In addition, the L103N Mhr displays unusually rapid reduction kinetics, suggesting that the amide functionality of Asn-103 destabilizes most bound ligands and additionally promotes rapid semi-met(R) ⇆ semi-met(O) isomerization.

Original languageEnglish (US)
Pages (from-to)7037-7043
Number of pages7
JournalBiochemistry
Volume36
Issue number23
DOIs
StatePublished - Jun 10 1997

ASJC Scopus subject areas

  • Biochemistry

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