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Applied and Environmental Microbiology, December 2005, p. 8706-8713, Vol. 71, No. 12
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.12.8706-8713.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Allelic Variation of Polymorphic Locus lytB, Encoding a Choline-Binding Protein, from Streptococci of the Mitis Group
Miriam Moscoso,
Virginia Obregón,,
Rubens López,
José L. García, and
Ernesto García*
Departamento de Microbiología Molecular, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain
Received 31 May 2005/ Accepted 27 July 2005
The choline-binding protein LytB, an N-acetylglucosaminidase of Streptococcus pneumoniae, is the key enzyme for daughter cell separation and is believed to play a critical pathogenic role, facilitating bacterial spreading during infection. Because of these peculiarities LytB is a putative vaccine target. To determine the extent of LytB polymorphism, the lytB alleles from seven typical, clinical pneumococcal isolates of various serotypes and from 13 additional streptococci of the mitis group (12 atypical pneumococci and the Streptococcus mitis type strain) were sequenced. Sequence alignment showed that the main differences among alleles were differences in the number of repeats (range, 12 to 18) characteristic of choline-binding proteins. These differences were located in the region corresponding to repeats 11 to 17. Typical pneumococcal strains contained either 14, 16, or 18 repeats, whereas all of the atypical isolates except strains 1283 and 782 (which had 14 and 16 repeats, respectively) and the S. mitis type strain had only 12 repeats; atypical isolate 10546 turned out to be a 
lytB mutant. We also found that there are two major types of alternating repeats in lytB, which encode 21 and 23 amino acids. Choline-binding proteins are linked to the choline-containing cell wall substrate through choline residues at the interface of two consecutive choline-binding repeats that create a choline-binding site. The observation that all strains contained an even number of repeats suggests that the duplication events that gave rise to the choline-binding repeats of LytB involved two repeats simultaneously, an observation that is in keeping with previous crystallographic data. Typical pneumococcal isolates usually grew as diplococci, indicating that an active LytB enzyme was present. In contrast, most atypical isolates formed long chains of cells that did not disperse after addition of purified LytB, suggesting that in these strains chains were produced through mechanisms unrelated to LytB.
* Corresponding author. Mailing address: Departamento de Microbiología Molecular, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, 28040 Madrid, Spain. Phone: (34) 91 837 3112. Fax: (34) 91 536 0432. E-mail: e.garcia{at}cib.csic.es.
M.M. and V.O. contributed equally to this work.
Present address: Bioferma Murcia S.A., Research Centre and Production, Parque Industrial Las Salinas, Avenida de Europa s/n, 30840 Alhama de Murcia, Spain.
Applied and Environmental Microbiology, December 2005, p. 8706-8713, Vol. 71, No. 12
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.12.8706-8713.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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