Molecular characterization of KEX1, a kexin-like protease in mouse Pneumocystis carinii

Expression screening of a Pneumocystis carinii-infected mouse lung cDNA lib rary with specific monoclonal antibodies (mAbs) led to the identification o f a P. carinii cDNA with extensive homology to subtilisin-like proteases, p articularly fungal kexins and mammalian prohormone convertases. The 3.1 kb cDNA contains a single open reading frame encoding 1011 amino acids. Struct ural similarities to fungal kexins in the deduced primary amino acid sequen ce include a putative proenzyme domain delineated by a consensus autocataly tic cleavage site (Arg-Glu-Lys-Arg), conserved Asp, His, Asn and Ser residu es in the putative catalytic domain, a hydrophobic transmembrane spanning d omain, and a carboxy-terminal cytoplasmic domain with a conserved tyrosine motif thought to be important for localization of the protease in the endop lasmic reticulum and/or Golgi apparatus. Based on these structural similari ties and the classification of P. carinii as a fungus, the protease was nam ed KEX1, Southern blotting of mouse P. carinii chromosomes localized kex1 t o a single chromosome of approximately 610 kb, Southern blotting of restric tion enzyme digests of genomic DNA from P. carinii-infected mouse lung demo nstrated that kex1 is a single copy gene. The function of kexins in other f ungi suggests that KEX1 may be involved in the post-translational processin g and maturation of other P. carinii proteins. (C) 2000 Elsevier Science B. V. All rights reserved.