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A 42kD actin filament severing and capping protein from Physarum polycephalum which shares many properties with severin and gelsolin but has in addition some rather surprising exclusive features. Actin in complex with fragmin has been found to be phosphorylated on threonines 202 and 203.  These residues are involved in contacts with DNAse 1 and actin itself so it is likely that this would result in an inhibition of polymerization, also it has been found that the kinase binds very tightly to the fragmin actin complex. Recently another fragmin like protein has been isolated from Physarum which has a molecular weight of 60kD.

Click here for a diagram of the domain structure of the Gelsolin/Villin family.


Ampe, C. and J. Vandekerckhove (1987). "The F-actin capping proteins of Physarum polycephalum: cap42(a) is very similar, if not identical, to fragmin and is structurally and functionally very homologous to gelsolin; cap42(b) is Physarum actin." EMBO J. 6, 4149-4157.

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