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Applied and Environmental Microbiology, May 2009, p. 3120-3126, Vol. 75, No. 10
0099-2240/09/$08.00+0     doi:10.1128/AEM.02271-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Identification of Natural Target Proteins Indicates Functions of a Serralysin-Type Metalloprotease, PrtA, in Anti-Immune Mechanisms{triangledown}

Gabriella Felföldi, Judit Marokházi, Miklós Képiró, and István Venekei*

Department of Biochemistry, Eötvös Loránd University, Budapest, Hungary

Received 2 October 2008/ Accepted 13 March 2009

Serralysins are generally thought to function as pathogenicity factors of bacteria, but so far no hard evidence of this (e.g., specific substrate proteins that are sensitive to the cleavage by these proteases) has been found. We have looked for substrate proteins to a serralysin-type proteinase, PrtA, in a natural host-pathogen molecular interaction system involving Manduca sexta and Photorhabdus luminescens. The exposure in vitro of hemolymph to PrtA digestion resulted in selective cleavage of 16 proteins, provisionally termed PAT (PrtA target) proteins. We could obtain sequence information for nine of these PrtA sensitive proteins, and by searching databases, we could identify six of them. Each has immune-related function involving every aspect of the immune defense: β-1,3 glucan recognition protein 2 (immune recognition), hemocyte aggregation inhibitor protein (HAIP), serine proteinase homolog 3, six serpin-1 variants, including serpin-1I (immune signaling and regulation), and scolexins A and B (coagulation cascade effector function). The functions of the identified PrtA substrate proteins shed new light on a possible participation of a serralysin in the virulence mechanism of a pathogen. Provided these proteins are targets of PrtA in vivo, this might represent, among others, a complex suppressive role on the innate immune response via interference with both the recognition and the elimination of the pathogen during the first, infective stage of the host-pathogen interaction. Our results also raise the possibility that the natural substrate proteins of serralysins of vertebrate pathogens might be found among the components of the innate immune system.

* Corresponding author. Mailing address: Department of Biochemistry, Eötvös University, Pázmány Péter sétány 1/C, Budapest 1117, Hungary. Phone: (36-1) 381-2171. Fax: (36-1) 381-2172. E-mail: venekei{at}elte.hu

{triangledown} Published ahead of print on 20 March 2009.

Applied and Environmental Microbiology, May 2009, p. 3120-3126, Vol. 75, No. 10
0099-2240/09/$08.00+0     doi:10.1128/AEM.02271-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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