AUTHOR=Roshini Janardhanaachari , Patro L. Ponoop Prasad , Sundaresan Sruthi , Rathinavelan Thenmalarchelvi 

TITLE=Structural diversity among Acinetobacter baumannii K-antigens and its implication in the in silico serotyping

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1191542

DOI=10.3389/fmicb.2023.1191542

ISSN=1664-302X

ABSTRACT=<p><italic>Acinetobacter baumannii</italic> is an emerging opportunistic pathogen. It exhibits multi-, extreme-, and pan-drug resistance against several classes of antibiotics. Capsular polysaccharide (CPS or K-antigen) is one of the major virulence factors which aids <italic>A. baumannii</italic> in evading the host immune system. K-antigens of <italic>A. baumannii</italic> exploit the Wzx/Wzy-dependent pathway that involves 13 different proteins for its assembly and transport onto the outer membrane. A total of 64 (out of 237 K-locus(KL) types) known K-antigen sugar repeating structures are discussed here and are classified into seven groups based on their initial sugars, QuiNAc4NAc, GalNAc, GlcNAc, Gal, QuiNAc/FucNAc, FucNAc, and GlcNAc along with Leg5Ac7Ac/Leg5Ac7R. Thus, the corresponding seven initializing glycosyltransferases (ItrA1, ItrA2, ItrA3, ItrA4, ItrB1, ItrB3, and ItrA3 along with ItrB2) exhibit serotype specificity. The modeled 3D-structural repository of the 64 K-antigens can be accessed at <ext-link ext-link-type="uri" xlink:href="https://project.iith.ac.in/ABSD/k_antigen.html" xmlns:xlink="http://www.w3.org/1999/xlink">https://project.iith.ac.in/ABSD/k_antigen.html</ext-link>. The topology of K-antigens further reveals the presence of 2-6 and 0-4 sugar monomers in the main and side chains, respectively. The presence of negatively (predominant) or neutrally charged K-antigens is observed in <italic>A. baumannii</italic>. Such diversity in the K-antigen sugar composition provides the K-typing specificity (<italic>viz</italic>., 18–69% in terms of reliability) for Wza, Wzb, Wzc, Wzx, and Wzy proteins involved in the Wzx/Wzy-dependent pathway. Interestingly, the degree of uniqueness of these proteins among different K-types is estimated to be 76.79%, considering the 237 reference sequences. This article summarizes the <italic>A. baumannii</italic> K-antigen structural diversity and creation of a K-antigen digital repository and provides a systematic analysis of the K-antigen assembly and transportation marker proteins.</p>