This entry represents Spire1, which belongs to the Spire family. It contains a KIND (kinase noncatalytic C-lobe) domain and four actin-binding WH2 (WASP homology 2) domains []. It acts as an actin nucleation factors []. The structure of Spire has been revealed [, ]. Spire1 is involved in intracellular vesicle transport along actin fibres, providing a novel link between actin cytoskeleton dynamics and intracellular transport []. The mammalian genome encodes two Spir proteins, Spir-1 and Spir-2. In adult tissues, the spir-2 gene shows a rather broad expression pattern, whereas spir-1 is mainly expressed in neuronal cells of the nervous system. Spir-1 may have a role in neural function [].
The KIND (kinase non-catalytic C-lobe domain) is a putative protein interaction domain, which has been identified as being similar to the C-terminal protein kinase catalytic fold (C lobe) (see ).The presence of the KIND domain at the N terminus of signalling proteins and the absence of the active site residues in the catalytic and activation loops suggest that it folds independently and is likely to be non-catalytic. The occurrence of the domain only in metazoa implies that it has evolved from the catalytic protein kinase domain into an interaction domain possibly by keeping the substrate-binding features [, ]. In SPIRE1 (protein spire homologue 1) this domain interacts with FMN2 (formin-2) [, ].
