CLAMP, a novel microtubule-associated protein with EB-type calponin homology

Abstract

Microtubules (MTs) are polymers of alpha and beta tubulin dimers that mediate many cellular functions, including the establishment and maintenance of cell shape. The dynamic properties of MTs may be influenced by tubulin isotype, posttranslational modifications of tubulin, and interaction with microtubule-associated proteins (MAPs). End-binding (EB) family proteins affect MT dynamics by stabilizing MTs, and are the only MAPs reported that bind MTs via a calponin-homology (CH) domain (J Biol Chem 278 (2003) 49721-49731; J Cell Biol 149 (2000) 761-766). Here, we describe a novel 27 kDa protein identified from an inner ear organ of Corti library. Structural homology modeling demonstrates a CH domain in this protein similar to EB proteins. Northern and Western blottings confirmed expression of this gene in other tissues, including brain, lung, and testis. In the organ of Corti, this protein localized throughout distinctively large and well-ordered MT bundles that support the elongated body of mechanically stiff pillar cells of the auditory sensory epithelium. When ectopically expressed in Cos-7 cells, this protein localized along cytoplasmic MTs, promoted MT bundling, and efficiently stabilized MTs against depolymerization in response to high concentration of nocodazole and cold temperature. We propose that this protein, designated CLAMP, is a novel MAP and represents a new member of the CH domain protein family.

Insights into EB1 structure and the role of its C-terminal domain for discriminating microtubule tips from the lattice

“…Similar to EBs, the two microtubule-binding, N-terminal CH domains of the Ndc80/Nuf2 complex are followed by a linker region and a coiled-coil dimerization domain (Supplemental Figure S9C). Furthermore, the same sequential arrangement of CH–linker–coiled coil is also found for the microtubule-binding protein Spef1/CLAMP (Supplemental Figure S9C; Dougherty et al , 2005). On the basis of these considerations, we hypothesize that interacting pairs of CH domains may represent a general property of microtubule-binding CH domains.…”

The CH-domain of Calponin does not Determine the Modes of Calponin Binding to F-actin

“…48 One example involves the EB (end-binding) family of microtubule-associated proteins, where it has been shown that the CH-domain within these proteins interact with microtubules. [49][50][51] The sequence and structure of actin are remarkably conserved, but actin-binding proteins do not show a similar degree of conservation. Structurally conserved domains found in actin-binding proteins may tell us more about the evolutionary relations among these proteins than about the function of these domains.…”

A yeast two hybrid screen identifies SPATA4 as a TRAPP interactor

“…The involvement of the DUF1042 domain in binding to C2 is interesting in light of the fact that this domain has been implicated in microtubule interactions [25]. Given that ER-derived carriers migrate along microtubule tracks [26], it is tempting to speculate that SPATA4 may link TRAPP to the microtubule network to facilitate membrane traffic in spermatocytes.…”