Phomopsin A

Phomopsin A is a cyclic hexapeptide mycotoxin that inhibits β-tubulin.

Phomopsins are a family of mycotoxins produced by the fungus Phomopsis leptostomiformis grows on lupins, which cause lupinosis, a severe liver disease of grazing animals [1][2].

Microtubules are one of the major components of the cytoskeleton that are essential in several cellular functions such as cell division and morphogenesis. α- and β-tubulins polymerize into microtubules.

Phomopsin A is a cyclic hexapeptide mycotoxin that binds β-tubulin in a vinca domain, partly overlapping with the site targeted by vinblastine and other tubulin inhibitors [2][3]. Phomopsin A noncompetitively inhibited the binding of radiolabeled vinblastine to tubulin with IC50 and Ki values of 0.8 μM and 2.8 μM, respectively. Phomopsin A potently inhibited tubulin-dependent GTP hydrolysis and nucleotide exchange on tubulin [2]. Phomopsin A, a vinca domain antimitotic peptide, also inhibited microtubule assembly [3][4]. Phomopsin A inhibited microtubule growth, modulated the dynamics of microtubules, and induced the self-association of tubulin dimers into single-walled rings and spirals [4].

References:
[1].  Hamel E. Natural products which interact with tubulin in the vinca domain: maytansine, rhizoxin, phomopsin A, dolastatins 10 and 15 and halichondrin B. Pharmacol Ther. 1992;55(1):31-51.
[2].  Cormier A, Marchand M, Ravelli RB, et al. Structural insight into the inhibition of tubulin by vinca domain peptide ligands. EMBO Rep. 2008 Nov;9(11):1101-6.
[3].  Li Y, Kobayashi H, Hashimoto Y, et al. Binding selectivity of rhizoxin, phomopsin A, vinblastine, and ansamitocin P-3 to fungal tubulins: differential interactions of these antimitotic agents with brain and fungal tubulins. Biochem Biophys Res Commun. 1992 Sep 16;187(2):722-9.
[4].  Mitra A, Sept D. Localization of the antimitotic peptide and depsipeptide binding site on beta-tubulin. Biochemistry. 2004 Nov 9;43(44):13955-62.