The mammalian S100A1 protein can activate the invertebrate myosin-associated giant protein kinase twitchin in a Ca2+-dependent manner by more than 1000-fold in vitro; however, no mammalian S100-dependent protein kinases are known. In an attempt to identify novel mammalian Ca2+/S100A1-regulated protein kinases, brain extracts were subjected to combined Ca2+-dependent affinity chromatography with S100A1 and an ATP analogue. This resulted in the purification to near-homogeneity of the four major synapsin isoforms Ia, Ib, IIa and IIb. All four synapsins were specifically affinity-labelled with the ATP analogue 5′-p-fluorosulphonylbenzoyladenosine. S100A1 bound to immobilized synapsin IIa in BIAcore experiments in a Ca2+-dependent and Zn2+-enhanced manner with submicromolar affinity; this interaction could be competed for with synthetic peptides of the proposed S100A1-binding sites of synapsin. Double-labelling confocal immunofluorescence microscopy demonstrated that synapsins and S100A1 are both present in the soma and neurites of PC12 cells, indicating their potential to interact in neurons in vivo.
Synapsins as major neuronal Ca2+/S100A1-interacting proteins
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Jörg HEIERHORST, Ken I. MITCHELHILL, Richard J. MANN, Tony TIGANIS, Andrew J. CZERNIK, Paul GREENGARD, Bruce E. KEMP; Synapsins as major neuronal Ca2+/S100A1-interacting proteins. Biochem J 1 December 1999; 344 (2): 577–583. doi: https://doi.org/10.1042/bj3440577
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