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First published online 12 August 2008
doi: 10.1242/jcs.026963

Journal of Cell Science 121, 2930-2938 (2008)
Published by The Company of Biologists 2008
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Research Article

Arginine deiminase has multiple regulatory roles in the biology of Giardia lamblia

Maria Carolina Touz1,*,{ddagger}, Andrea Silvana Rópolo1,*, Maria Romina Rivero1, Cecilia Veronica Vranych1, John Thomas Conrad2, Staffan Gunnar Svard3 and Theodore Elliott Nash2

1 Instituto de Investigación Medica Mercedes y Martín Ferreyra, INIMEC – CONICET, Friuli 2434, Cordoba, Argentina
2 Laboratory of Parasitic Diseases, NIAID, NIH, Bethesda, MD 20892, USA
3 Department of Cell and Molecular Biology, Uppsala University, SE-75 124 Uppsala, Sweden.

{ddagger} Author for correspondence (e-mail: ctouz{at}immf.uncor.edu)

Accepted 16 June 2008

The protozoan parasite Giardia lamblia uses arginine deiminase (ADI) to produce energy from free L-arginine under anaerobic conditions. In this work, we demonstrate that, in addition to its known role as a metabolic enzyme, it also functions as a peptidylarginine deiminase, converting protein-bound arginine into citrulline. G. lamblia ADI specifically binds to and citrullinates the arginine in the conserved CRGKA tail of variant-specific surface proteins (VSPs), affecting both antigenic switching and antibody-mediated cell death. During encystation, ADI translocates from the cytoplasm to the nuclei and appears to play a regulatory role in the expression of encystation-specific genes. ADI is also sumoylated, which might modulate its activity. Our findings reveal a dual role played by ADI and define novel regulatory pathways used by Giardia for survival.

Key words: Arginine deiminase, Citrullination, Sumoylation, Antigenic variation, Encystation, Gene regulation






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