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.
-Agglutinin and a-Agglutinin,
Saccharomyces cerevisiae Sexual Cell Adhesion
Molecules

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