Unique Properties of Heme Binding of the Porphyromonas gingivalis HmuY Hemophore-like Protein Result from the Evolutionary Adaptation of the Protein Structure.

Joanna Kosno,Teresa Olczak,Klaudia Siemińska

doi:10.3390/molecules27051703

Abstract

To acquire heme, Porphyromonas gingivalis uses a hemophore-like protein (HmuY). HmuY sequesters heme from host hemoproteins or heme-binding proteins produced by cohabiting bacteria, and delivers it to the TonB-dependent outer-membrane receptor (HmuR). Although three-dimensional protein structures of members of the novel HmuY family are overall similar, significant differences exist in their heme-binding pockets. Histidines (H134 and H166) coordinating the heme iron in P. gingivalis HmuY are unique and poorly conserved in the majority of its homologs, which utilize methionines. To examine whether changes observed in the evolution of these proteins in the Bacteroidetes phylum might result in improved heme binding ability of HmuY over its homologs, we substituted histidine residues with methionine residues. Compared to the native HmuY, site-directed mutagenesis variants bound Fe(III)heme with lower ability in a similar manner to Bacteroides vulgatus Bvu and Tannerella forsythia Tfo. However, a mixed histidine-methionine couple in the HmuY was sufficient to bind Fe(II)heme, similarly to T. forsythia Tfo, Prevotella intermedia PinO and PinA. Double substitution resulted in abolished heme binding. The structure of HmuY heme-binding pocket may have been subjected to evolution, allowing for P. gingivalis to gain an advantage in heme acquisition regardless of environmental redox conditions.

Highlights

The development of periodontal diseases is linked with an environmental shift in members of the oral microbiome, leading to the domination of Gram-negative pathogenic bacteria over early Gram-positive commensal colonizers, with species of aerobic Streptococcus being the most abundant [1,2]
Bacterial species isolated from subgingival samples associated with the clinical features of chronic periodontitis are characterized by the presence of increased numbers of anaerobic bacteria classified in the red complex, i.e., Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola [1,3–6]
HmuY sequesters heme from host hemoproteins or heme-binding proteins produced by cohabitating bacteria and delivers it to the TonB-dependent outermembrane receptor (HmuR), which transports heme through the outer membrane [16]

Summary

Introduction

The development of periodontal diseases is linked with an environmental shift in members of the oral microbiome, leading to the domination of Gram-negative pathogenic bacteria over early Gram-positive commensal colonizers, with species of aerobic Streptococcus being the most abundant [1,2]. Bacterial species isolated from subgingival samples associated with the clinical features of chronic periodontitis are characterized by the presence of increased numbers of anaerobic bacteria classified in the red complex, i.e., Porphyromonas gingivalis (formerly Bacteroides gingivalis), Tannerella forsythia (formerly Bacteroides forsythus), and Treponema denticola [1,3–6]. Other bacteria, such as Prevotella intermedia, a member of the orange complex, serve as early dental plaque colonizers and bridging species with members of the red complex, mainly aiding in creation of an environment that allows for the colonization of subgingival plaque [4,5]. HmuY sequesters heme from host hemoproteins or heme-binding proteins produced by cohabitating bacteria and delivers it to the TonB-dependent outermembrane receptor (HmuR), which transports heme through the outer membrane [16]

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