Phosphorylation of amphiphysin I by minibrain kinase/dual-specificity tyrosine phosphorylation-regulated kinase, a kinase implicated in Down syndrome.

Minibrain kinase/dual-specificity tyrosine phosphorylation-regulated kinase (Mnb/Dyrk1A) is a proline-directed serine/threonine kinase encoded in the Down syndrome critical region of human chromosome 21. This kinase has been shown to phosphorylate dynamin 1 and synaptojanin 1. Here we report that amphiphysin I (Amph I) is also a Mnb/Dyrk1A substrate.

Structure of the light chain-binding domain of myosin V.

Myosin V is a double-headed molecular motor involved in organelle transport. Two distinctive features of this motor, processivity and the ability to take extended linear steps of approximately 36 nm along the actin helical track, depend on its unusually long light chain-binding domain (LCBD). The LCBD of myosin V consists of six tandem IQ motifs, which constitute the binding sites for calmodulin (CaM) and CaM-like light chains.

Myosin V attachment to cargo requires the tight association of two functional subdomains.

The myosin V carboxyl-terminal globular tail domain is essential for the attachment of myosin V to all known cargoes. Previously, the globular tail was viewed as a single, functional entity. Here, we show that the globular tail of the yeast myosin Va homologue, Myo2p, contains two structural subdomains that have distinct functions, namely, vacuole-specific and secretory vesicle-specific movement.

Two distinct myosin light chain structures are induced by specific variations within the bound IQ motifs-functional implications.

IQ motifs are widespread in nature. Mlc1p is a calmodulin-like myosin light chain that binds to IQ motifs of a class V myosin, Myo2p, and an IQGAP-related protein, Iqg1p, playing a role in polarized growth and cytokinesis in Saccharomyces cerevisiae. The crystal structures of Mlc1p bound to IQ2 and IQ4 of Myo2p differ dramatically.

Crystallization, X-ray characterization and selenomethionine phasing of Mlc1p bound to IQ motifs from myosin V.

Mlc1p is a calmodulin-like protein from the budding yeast Saccharomyces cerevisiae, where it has been identified as a subunit of a class V myosin, Myo2p, and a binding partner of an IQGAP-like protein, Iqg1p. Through its interactions with these two proteins, Mlc1p plays a role in polarized growth and cytokinesis. Mlc1p has been crystallized in complexes with four different IQ target motifs from the neck region of Myo2p: IQ2, IQ3, IQ4 and IQ2-IQ3 (referred to as IQ2,3).