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Infection and Immunity, September 2001, p. 5494-5501, Vol. 69, No. 9
Department of Biochemistry and Molecular
Biology, University of Georgia, Athens,
Georgia,1 Department of Microbiology and
Immunology, Jagiellonian University, Cracow,
Poland,2 and Department of
Biological, Geological, and Environmental Sciences, Cleveland State
University, Cleveland, Ohio3
Received 20 April 2001/Returned for modification 28 May
2001/Accepted 15 June 2001
Streptococcus gordonii is generally considered a
benign inhabitant of the oral microflora, and yet it is a primary
etiological agent in the development of subacute bacterial endocarditis
(SBE), an inflammatory state that propagates thrombus formation and
tissue damage on the surface of heart valves. Strain FSS2 produced
several extracellular aminopeptidase and fibrinogen-degrading
activities during growth in culture. In this report we describe the
purification, characterization, and cloning of a serine class
dipeptidyl-aminopeptidase, an x-prolyl dipeptidyl-peptidase
(Sg-xPDPP, for S. gordonii x-prolyl dipeptidyl-peptidase), produced in a pH-controlled
batch culture. Purification of this enzyme by anion exchange, gel
filtration, and hydrophobic interaction chromatography yielded a
protein monomer of approximately 85 kDa, as shown by sodium dodecyl
sulfate-polyacrylamide gel electrophoresis (PAGE) under denaturing
conditions. However, under native conditions, the protein appeared to
be a homodimer on the basis of gel filtration and PAGE. Kinetic studies
indicated that purified enzyme had a unique and stringent x-prolyl
specificity that is comparable to both the dipeptidyl-peptidase IV/CD26
and lactococcal x-prolyl dipeptidyl-peptidase families. Nested PCR cloning from an S. gordonii library enabled the
isolation and sequence analysis of the full-length gene. A
759-amino-acid polypeptide with a theoretical molecular mass of 87,115 Da and a calculated pI of 5.6 was encoded by this open reading frame.
Significant homology was found with the PepX gene family from
Lactobacillus and Lactococcus spp. and
putative x-prolyl dipeptidyl-peptidases from other streptococcal
species. Sg-xPDPP may serve as a critical factor for the
sustained bacterial growth in vivo and furthermore may aid in the
proteolysis of host tissue that is commonly observed during SBE pathology.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.9.5494-5501.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Novel Extracellular x-Prolyl Dipeptidyl-Peptidase
(DPP) from Streptococcus gordonii FSS2: an Emerging
Subfamily of Viridans Streptococcal x-Prolyl DPPs
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602-7229. Phone: (706) 542-1713. Fax: (706) 542-3719. E-mail: jtravis{at}arches.uga.edu.
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