The antigenicity and cholesteroid nature of mycolic acids determined by recombinant chicken antibodies

PLoS One. 2018 Aug 9;13(8):e0200298. doi: 10.1371/journal.pone.0200298. eCollection 2018.

Abstract

Mycolic acids (MA) are major, species-specific lipid components of Mycobacteria and related genera. In Mycobacterium tuberculosis, it is made up of alpha-, methoxy- and keto-MA, each with specific biological functions and conformational characteristics. Antibodies in tuberculosis (TB) patient sera respond differently towards the three MA classes and were reported to cross-react with cholesterol. To understand the antigenicity and cholesterol cross-reactivity of MA, we generated three different chicken -derived phage-displayed single-chain variable fragments (scFv) that reacted similarly towards the natural mixture of MA, but the first recognized all three classes of chemically synthetic MAs, the second only the two oxygenated types of MAs and the third only methoxy MA. The cholesterol cross-reactivity was investigated after grafting each of the three scFv types onto two configurations of constant chain domains-CH1-4 and CH2-4. Weak but significant cross-reactivity with cholesterol was found only with CH2-4 versions, notably those two that were also able to recognize the trans-keto MA. The cholesteroid nature of mycobacterial mycolic acids therefore seems to be determined by the trans-keto MA subclass. The significantly weaker binding to cholesterol in comparison to MA confirms the potential TB diagnostic application of these antibodies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Avian Proteins / immunology
  • Chickens
  • Cholesterol / chemistry
  • Cholesterol / immunology*
  • Cross Reactions
  • Enzyme-Linked Immunosorbent Assay
  • HEK293 Cells
  • Humans
  • Molecular Structure
  • Mycobacterium tuberculosis / immunology*
  • Mycolic Acids / chemical synthesis
  • Mycolic Acids / chemistry
  • Mycolic Acids / immunology*
  • Protein Binding
  • Protein Engineering
  • Recombinant Proteins
  • Sensitivity and Specificity
  • Single-Chain Antibodies / immunology*

Substances

  • Avian Proteins
  • Mycolic Acids
  • Recombinant Proteins
  • Single-Chain Antibodies
  • Cholesterol

Grants and funding

This study was partly funded by the Council for Scientific and Industrial Research (CSIR) parliamentary grants (YL) and the National Research Foundation of South Africa for the grants, unique grant numbers: 99386 (HR), 88622, 80577 (YL) and TTK1206281756 (LN). Any opinion, finding and conclusion or recommendation expressed in this material is that of the authors and the NRF does not accept any liability in this regard; https://www.csir.co.za/; http://www.nrf.ac.za/. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.