Identification of Two Heme-Binding Sites in the Cytoplasmic Heme-Trafficking Protein PhuS from Pseudomonas aeruginosa and Their Relevance to Function

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• 作者：Darci R. Block ; Gudrun S. Lukat-Rodgers ; Kenton R. Rodgers ; Angela Wilks ; Mehul N. Bhakta ; Ila B. Lansky
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：December 18, 2007
• 年：2007
• 卷：46
• 期：50
• 页码：14391 - 14402
• 全文大小：502K
• 年卷期：v.46,no.50(December 18, 2007)
• ISSN：1520-4995

文摘

PhuS is a cytoplasmic, 39 kDa heme-binding protein from Pseudomonas aeruginosa. It haspreviously been shown to transfer heme to its cognate heme oxygenase. It is expressed from the phuoperon, which encodes a group of proteins known to actively internalize and transport heme from hostorganisms. This study combines the spectral resolution of resonance Raman spectroscopy with site-directedmutagenesis to identify and characterize the heme-bound states of holo-PhuS. This combined approachhas identified a site in monomeric PhuS having alternate His ligands at positions 209 and 212. A seconddistinct binding site is present in dimeric PhuS. This site supports six-coordinate, low-spin heme, evenwhen both His209 and His212 are mutated to Ala. The presence of conserved His and Tyr residues in allof the homologs characterized to date suggest that the dimer could be of the domain-swapped type inwhich two protein molecules are cross-linked by bound heme. The multiple heme-bound states and theirsensitivity to pH suggest the possibility that these cytoplasmic heme-binding proteins have multiple functionsthat are toggled by variations in intracellular conditions.