Identification and immunogenic properties of recombinant ZnuD protein loops of Acinetobacter baumannii

Abstract

Background: Pan-drug-resistant Acinetobacter baumannii is one of the three major priorities to control and treat, as announced by the World Health Organization (WHO). Transition metals such as zinc are critical elements in pathogen-host interaction. They have a critical role in A.baumannii physiology and pathogenicity as a cofactor of many enzymes and DNA-binding proteins. To survive and establish infection under zinc-limited conditions, an outer membrane receptor, ZnuD, is expressed to play a vital role in the acquisition of zinc. This virulence factor could also induce protective antibodies in convalescent patient sera recovered from meningococcal infections. Methods: In this study, the physicochemical properties, and secondary and tertiary structures, of A.baumannii ATCC 19606 ZnuD were analyzed by in silico approaches. The potential of ZnuD in binding zinc was assessed by molecular docking, and conformational instability was calculated by a molecular dynamics (MD) simulation. Antigenic loops containing immune epitopes were also evaluated by epitope mapping servers. Results: In silico analyses demonstrated that this receptor is conserved among 1200 A.baumannii species, and is a stable Outer Membrane Protein (OMP) belonging to the TonB dependent receptor (TBDR) with 22 β-strands, 11 outer membrane loops, and 10 turns. This receptor has an evolutionary relationship with ZnuD of N.meningitidis. Docking analyses demonstrated that ZnuD was involved in binding zinc, and could have an equilibration state under this condition. Epitope mapping results demonstrated several immunogenic conserved epitopes in eight exposed loops. Conclusion: The results indicated that ZnuD and most of its antigenic loops are potentially suitable antigens for subunit vaccine development approaches.

Keywords

• Acinetobacter baumannii
• ZnuD
• OMP
• TonB
• Vaccine