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First published online June 29, 2006
Journal of Experimental Biology 209, 2651-2659 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02267

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A novel secreted endonuclease from Culex quinquefasciatus salivary glands

Eric Calvo and José M. C. Ribeiro^*

Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Twinbrook III (12735 Twinbrook Parkway), Room 2E-32D, Rockville, MD 20852, USA

^* Author for correspondence (e-mail: jribeiro{at}niaid.nih.gov)

Accepted 13 April 2006

Previous analysis of the salivary gland transcriptome of Culex quinquefasciatus showed the potential presence of an endonuclease with sequence similarities to shrimp, crab and two tsetse salivary proteins. Indeed, not only was the cloned cDNA shown to encode an active double-stranded endonuclease, but also the same activity was demonstrated to be secreted by salivary glands of Cx. quinquefasciatus. Preliminary studies with salivary gland extracts confirmed the presence of a highly active nuclease. This enzyme was shown to be present in the saliva of female mosquitoes by allowing starved mosquitoes to probe DNA-containing agarose gel. The recombinant Cx. quinquefasciatus endonuclease (CuquEndo) produced in mammalian cells showed no sequence specificity for DNA substrate except that it only cleaves double-stranded DNA. Recombinant Cx. quinquefasciatus endonuclease was active in the presence of Mg²⁺ ions at pH 7.0-8.0, but no endonuclease activity was detected in the presence of calcium ions. The final hydrolysis products of this enzyme, detected by ion exchange chromatography, yielded DNA fragments ranging form 8-12 base pairs. Although endonucleases have been associated with a variety of cellular functions, their role in mosquito saliva is not clear. This female-specific secreted endonuclease may assist blood meal intake by lowering the local viscosity created by the release of host DNA in the bite site and/or acting as an indirect anticoagulant factor by producing a defibrotide-like mixture of DNA haptamers.

Key words: mosquito, salivary gland, endonuclease, Culex quinquefasciatus, arthropod