Glossary Term: Catch Bond
A catch bond is a type of noncovalent bond which “breaks” less frequently as tensile force(s) applied to the bond are increased [1]. Catch bonds
were originally proposed to explain the interaction between molecules
such as L-selectin:PSGL-1; the bond between them has a lifetime that
increases as step loads are applied between 0 and ~25 pN, and they fall
exponentially at higher loads [2]. Although catch bonds were originally
found using atomic force microscopy, subsequent assays with biomembrane
force probes and shear flow assays [3] lend support to the concept that
certain bonds become stronger as force is applied.
Catch bonds vs slip bonds:
From
an experimental point of view, catch bonds are frequently compared with
slip bonds, which exhibit the opposite behavior when force is applied
(e.g. the average bond lifetime of slip bonds is shorter at higher forces, presumably because force pulls out the ligand).
In contrast to slip bonds, the average bond lifetime of catch bonds
increases with force up to a critical force. However, above the critical
force, even catch bonds enter a slip regime where force shortens the
dissociation lifetime, presumably because further force overpowers the
activated bonds [4, 5].
Measuring bond strength and dissociation lifetime:
Bond strength/dissociation is measured using isotonic experiments in which force is loaded to a constant level and held until the bond breaks. It is thought that the receptor and ligand are pulled apart steadily, so that force increases until the bond ruptures [6, 7]. In these experiments a distribution of rupture force(s) is established and any distinctive peaks are use to identify the bonds that break most frequently or are the shortest lived. This means slip bonds are characterized by a single peak at higher forces [8], while catch bonds can have two peaks, above and below the critical force [6, 7]. Because a bond will only break below the critical force if given enough time, the proportion of ruptures will also depend on how quickly the force is increased.
Examples of proteins that form catch bonds:
At least two types of adhesive proteins have been shown to form catch bonds: blood proteins called selectins [2] and a bacterial protein called FimH [9]. These proteins mediate shear-enhanced adhesion, which allows the cell to bind more strongly at high shear than at low shear. Within this context, catch bonds may bolster resistance to shear forces by recruiting more bonds where they are needed in a manner that resembles nanoscale “locking seat belts”. It has recently been demonstrated that catch bonds also exist between an integrin and its ligand [10].
Ĉ ď Sruthi Jaganathan, Jan 15, 2012 6:10 PM Ĉ ď Sruthi Jaganathan, Jan 15, 2012 6:11 PM
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