Coronin structure and implications

Abstract

Until recently, structural information about coronins was scarce and the earlier identification of five WD40 repeats gave rise to a structural prediction of a five-bladed β propeller for the N-terminal domain of these proteins. More detailed analyses revealed the presence of seven WD40 repeats and the hypothesis of a seven-bladed β propeller structure. This model has recendy been validated due to structural information fi-om crystal structures of C-terminally truncated coronin 1 (1 A), as well as its C-terminal coiled coil domain. Further structural information is available only indirectly from binding and functional studies. Phosphorylation at distinct serine and tyrosine residues seems to be a common theme for various coronins. There are indications that this modification regulates the quaternary structure of coronin 3 (IC) and thus has imlications for the cellular localisation and the general Unk between signalling and cytoskeletal remodelling. Similarly, phosphorylation-dependent sorting sequences recendy discovered on coronin 7 might prove important for the molecular mechanisms of the longer coronins. A matter that will require further clarification is the localisation of protein binding sites on coronins. While earlier reports presented a rather diverse map of actin binding sites, more recent studies, including the crystal structure of the coronin 1 N-terminal domain, deliver more detailed information in this respect. Interaaion sites for other target proteins, such as Arp2/3, remain to be identified. Also, while membrane binding is a known feature of coronins, further details as to the binding sites and molecular level events remain to be elucidated. The N-terminal WD40 repeat domain seems to be the membrane-interacting domain, but other domains might provide regulatory effects, most likely by posttranslational modification, in a fashion that is specific for each coronin. In this chapter, we provide a structural overview of coronins 1 (lA), 2 (IB), 3 (IC) and 7 and also present results of our recent efforts to obtain structural models of coronins 3 and 7. Possible implications of these models on the function of these proteins are discussed.