Structural highlights
FunctionCYCP_ALCXX Cytochrome c' is the most widely occurring bacterial c-type cytochrome. Cytochromes c' are high-spin proteins and the heme has no sixth ligand. Their exact function is not known. Publication Abstract from PubMedCytochromes c', that occur in methanotrophic, denitrifying and photosynthetic bacteria, form unusual proximal penta-coordinate NO complexes via a hexa-coordinate distal NO intermediate. Their NO binding properties are similar to those of the eukaryotic NO sensor, soluble guanylate cyclase, for which they provide a valuable structural model. Previous studies suggested that hydrogen bonding between the displaced proximal histidine (His120) ligand (following its dissociation from heme due to trans effects from the distally bound NO) and a conserved aspartate residue (Asp121) could play a key role in allowing proximal NO binding to occur. We have characterized three variants of Alcaligenes xylosoxidans cytochrome c' (AXCP) where Asp121 has been replaced by Ala, Ile and Gln, respectively. In all variants, hydrogen bonding between residue 121 and His120 is abolished yet 5-coordinate proximal NO species are still formed. Our data therefore demonstrate that the His120-Asp121 bond is not essential for proximal NO binding although it likely provides an energy minimum for the displaced His ligand. All variants have altered proximal pocket structure relative to native AXCP. Hydrogen bonding of the dissociated histidine ligand is not required for formation of a proximal NO adduct in cytochrome c'.,Ghafoor DD, Kekilli D, Abdullah GH, Dworkowski FS, Hassan HG, Wilson MT, Strange RW, Hough MA J Biol Inorg Chem. 2015 Sep;20(6):949-56. doi: 10.1007/s00775-015-1278-y. Epub, 2015 Jun 23. PMID:26100643[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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