Plasmodium falciparum liver stage antigen-1 is cross-linked by tissue transglutaminase

Nicoll, W.S., Sacci, J.B., Rodolfo, C., Holland, Z.J.M., Doerig, C., Hollingdale, M.R. and Lanar, D.E. (2011) Plasmodium falciparum liver stage antigen-1 is cross-linked by tissue transglutaminase. Malaria Journal, 10(1), p. 14. (doi: 10.1186/1475-2875-10-14)

Abstract

Background Plasmodium falciparum sporozoites injected by mosquitoes into the blood rapidly enter liver hepatocytes and undergo pre-erythrocytic developmental schizogony forming tens of thousands of merozoites per hepatocyte. Shortly after hepatocyte invasion, the parasite starts to produce Liver Stage Antigen-1 (LSA-1), which accumulates within the parasitophorous vacuole surrounding the mass of developing merozoites. The LSA-1 protein has been described as a flocculent mass, but its role in parasite development has not been determined. Methods Recombinant N-terminal, C-terminal or a construct containing both the N- and C- terminal regions flanking two 17 amino acid residue central repeat sequences (LSA-NRC) were subjected to in vitro modification by tissue transglutaminase-2 (TG2) to determine if cross-linking occurred. In addition, tissue sections of P. falciparum-infected human hepatocytes were probed with monoclonal antibodies to the isopeptide ε-(γ-glutamyl)lysine cross-bridge formed by TG2 enzymatic activity to determine if these antibodies co-localized with antibodies to LSA-1 in the growing liver schizonts. Results This study identified a substrate motif for (TG2) and a putative casein kinase 2 phosphorylation site within the central repeat region of LSA-1. The function of TG2 is the post-translational modification of proteins by the formation of a unique isopeptide ε-(γ-glutamyl)lysine cross-bridge between glutamine and lysine residues. When recombinant LSA-1 protein was crosslinked in vitro by purified TG2 in a calcium dependent reaction, a flocculent mass of protein was formed that was highly resistant to degradation. The cross-linking was not detectably affected by phosphorylation with plasmodial CK2 in vitro. Monoclonal antibodies specific to the very unique TG2 catalyzed ε- lysine cross-bridge co-localized with antibodies to LSA-1 in infected human hepatocytes providing visual evidence that LSA-1 was cross-linked in vivo. Conclusions While the role of LSA-1 is still unknown these results suggest that it becomes highly cross-linked which may aid in the protection of the parasite as it develop

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Doerig, Dr Christian
• Authors: Nicoll, W.S., Sacci, J.B., Rodolfo, C., Holland, Z.J.M., Doerig, C., Hollingdale, M.R., and Lanar, D.E.
• College/School: College of Medical Veterinary and Life Sciences > School of Infection & Immunity
• Journal Name: Malaria Journal
• Journal Abbr.: Malar. J.
• Publisher: BioMed Central
• ISSN: 1475-2875
• Copyright Holders: Copyright © 2011 The Authors.
• First Published: First published in Malaria Journal 2011. 10(1):14
• Publisher Policy: Open Access article distributed under the terms of the Creative Commons Attribution License

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