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Journal of Bacteriology, May 2001, p. 2874-2880, Vol. 183, No. 9
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.9.2874-2880.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Interaction of alpha -Agglutinin and a-Agglutinin, Saccharomyces cerevisiae Sexual Cell Adhesion Molecules

Hui Zhao,1,dagger Zheng-Ming Shen,1 Peter C. Kahn,2 and Peter N. Lipke1,*

Department of Biological Sciences and the Institute for Biomolecular Structure and Function, Hunter College of the City University of New York, New York, New York 10021,1 and Department of Biochemistry and Microbiology, Cook College, Rutgers University, New Brunswick, New Jersey 089012

Received 6 November 2000/Accepted 7 February 2001

alpha -Agglutinin and a-agglutinin are complementary cell adhesion glycoproteins active during mating in the yeast Saccharomyces cerevisiae. They bind with high affinity and high specificity: cells of opposite mating types are irreversibly bound by a few pairs of agglutinins. Equilibrium and surface plasmon resonance kinetic analyses showed that the purified binding region of alpha -agglutinin interacted similarly with purified a-agglutinin and with a-agglutinin expressed on cell surfaces. At 20°C, the KD for the interaction was 2 × 10-9 to 5 × 10-9 M. This high affinity was a result of a very low dissociation rate (approx  2.6 × 10-4 s-1) coupled with a low association rate (= 5 × 104 M-1 s-1). Circular-dichroism spectroscopy showed that binding of the proteins was accompanied by measurable changes in secondary structure. Furthermore, when binding was assessed at 10°C, the association kinetics were sigmoidal, with a very low initial rate. An induced-fit model of binding with substantial apposition of hydrophobic surfaces on the two ligands can explain the observed affinity, kinetics, and specificity and the conformational effects of the binding reaction.

* Corresponding author. Mailing address: Department of Biological Sciences, Hunter College, 695 Park Ave., New York, NY 10021. Phone: (212) 772-5235. Fax: (212) 772-5227. E-mail: lipke{at}genectr.hunter.cuny.edu.

dagger Present address: Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115.

Journal of Bacteriology, May 2001, p. 2874-2880, Vol. 183, No. 9
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.9.2874-2880.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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