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The structured core of human ? tubulin confers isotype-specific polymerization properties.

ABSTRACT: Diversity in cytoskeleton organization and function may be achieved through variations in primary sequence of tubulin isotypes. Recently, isotype functional diversity has been linked to a "tubulin code" in which the C-terminal tail, a region of substantial sequence divergence between isotypes, specifies interactions with microtubule-associated proteins. However, it is not known whether residue changes in this region alter microtubule dynamic instability. Here, we examine recombinant tubulin with human ? isotype IIB and characterize polymerization dynamics. Microtubules with ?IIB have catastrophe frequencies approximately threefold lower than those with isotype ?III, a suppression similar to that achieved by regulatory proteins. Further, we generate chimeric ? tubulins with native tail sequences swapped between isotypes. These chimeras have catastrophe frequencies similar to that of the corresponding full-length construct with the same core sequence. Together, our data indicate that residue changes within the conserved ? tubulin core are largely responsible for the observed isotype-specific changes in dynamic instability parameters and tune tubulin's polymerization properties across a wide range.

SUBMITTER: Pamula MC

PROVIDER: S-EPMC4878094 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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The structured core of human β tubulin confers isotype-specific polymerization properties.

Pamula Melissa C MC Ti Shih-Chieh SC Kapoor Tarun M TM

The Journal of cell biology 20160516 4

Diversity in cytoskeleton organization and function may be achieved through variations in primary sequence of tubulin isotypes. Recently, isotype functional diversity has been linked to a "tubulin code" in which the C-terminal tail, a region of substantial sequence divergence between isotypes, specifies interactions with microtubule-associated proteins. However, it is not known whether residue changes in this region alter microtubule dynamic instability. Here, we examine recombinant tubulin with ...[more]

PMID: 27185835

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Project description:Tubulin, the basic component of microtubules, is present in most eukaryotic cells as multiple gene products, called isotypes. The major tubulin isotypes are highly conserved in terms of structure and drug binding capabilities. Tubulin isotype betaVI, however, is significantly divergent from the other isotypes in sequence, assembly properties, and function. It is the major beta-tubulin isotype of hematopoietic tissue and forms the microtubules of platelet marginal bands. The interaction of the major tubulin isotypes betaI, betaII, betaIII, and betaIotaV with antimicrotubule drugs has been widely studied, but little is known about the drug binding properties of tubulin isotype betaVI. In this investigation, we characterize the activity of various colchicine site ligands with tubulin isolated from Gallus gallus erythrocytes (CeTb), which is approximately 95% betaVI. Colchicine binding is thought to be a universal property of higher eukaryotic tubulin; however, we were unable to detect colchicine binding to CeTb under any experimental conditions. Podophyllotoxin and nocodazole, other colchicine site ligands with divergent structures, were able to inhibit paclitaxel-induced CeTb assembly. Surprisingly, the colchicine isomer allocolchicine also inhibited CeTb assembly and displayed measurable, moderate affinity for CeTb (K(a) = 0.18 x 10(5) M(-1) vs 5.0 x 10(5) M(-1) for bovine brain tubulin). Since allocolchicine and colchicine differ in their C ring structures, the two C ring colchicine analogues were also tested for CeTb binding. Kinetic experiments indicate that thiocolchicine and chlorocolchicine bind to CeTb, but very slowly and with low affinity. Molecular modeling of CeTb identified five divergent amino acid residues within 6 A of the colchicine binding site compared to betaI, betaII, and betaIV; three of these amino acids are also altered in betaIII-tubulin. Interestingly, the altered amino acids are in the vicinity of the A ring region of the colchicine binding site rather than the C ring region. We propose that the amino acid differences in the binding site constrict the A ring binding domain in CeTb, which interferes with the positioning of the trimethoxyphenyl A ring and prevents C ring binding site interactions from efficiently occurring. Allocolchicine is able to accommodate the altered binding mode because of its smaller ring size and more flexible C ring substituents. The sequence of the colchicine binding domain of CeTb isotype betaVI is almost identical to that of its human hematopoietic counterpart. Thus, through analysis of the interactions of ligands with CeTb, it may be possible to discover colchicine site ligands that specifically target tubulin in human hematopoietic cells.

Dataset Information

The structured core of human ? tubulin confers isotype-specific polymerization properties.

Publications

The structured core of human β tubulin confers isotype-specific polymerization properties.

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