1.A.71 The Brain Acid-soluble Protein Channel (BASP1 Channel) Family
BASP1 (also known as CAP-23 and NAP-22) is a brain abundant myristoylated protein localized at the inner surface of the presynaptic plasma membrane. Emerging evidence suggests that BASP1 is critically involved in various cellular processes, in particular, in the accumulation of phosphatidylinositol-4,5-diphosphate (PIP(2)) in lipid raft microdomains. Ostroumova et al. (2011) showed that BASP1 forms heterogeneously-sized oligomers and higher aggregates with an outward similarity to oligomers and protofibrils of amyloid proteins. BASP1 induces single channel currents across negatively-charged planar lipid bilayers. In this respect, BASP1 channels are similar to amyloid protein channels. BASP1 channels exhibit multiple conductance levels, in the range 10-3000 pS, with the most frequently observed conductance state of approximately 50 pS. The channels demonstrate a linear current-voltage relationship with voltage-independent kinetics of opening and closing. Their K+ to Cl- permeability ratio is approximately 14, showing that BASP1 channels are cation-selective. The ion channel activity of BASP1 is in accordance with the pore-like structure of BASP1 oligomers observed by electron microscopy on a lipid monolayer. Neuronal protein GAP-43, which is functionally related to BASP1 and also forms oligomers, elicited no ion channel currents under the conditions used.
The generalized reaction catalyzed by BASP1 is:
ions (in) %u21CC ions(out) (cation-selective)
Brain acid soluble protein, BASP1. (Ostroumova et al., 2011)
BASP1 of Homo sapiens (P80723)
Growth-associated protein 43 (GAP-43); Neuromodulin isoform 2, neural phosphoprotein B-50; A major component of the motile """"growth cones"""" that forms the tips of elongated axons. Binds calmodulin with high affinity without Ca2+ and low affinity with Ca2+. It has been reported not to form channels (Ostroumova et al., 2011). It has been reviewed (Holahan 2017).
GAP-43 of Homo sapiens (P17677)