Proteolytic processing of the L-type Ca2+ channel alpha11.2 subunit in neurons

Abstract

<ns4:p> <ns4:bold>Background</ns4:bold> : The L-type Ca2+ channel Cav1.2 is a prominent regulator of neuronal excitability, synaptic plasticity, and gene expression. The central element of Cav1.2 is the pore-forming α <ns4:sub>1</ns4:sub> 1.2 subunit. It exists in two major size forms, whose molecular masses have proven difficult to precisely determine. Recent work suggests that α <ns4:sub>1</ns4:sub> 1.2 is proteolytically cleaved between the second and third of its four pore-forming domains (Michailidis <ns4:italic>et al</ns4:italic> ,. 2014). </ns4:p> <ns4:p> <ns4:bold>Methods</ns4:bold> : To better determine the apparent molecular masses (M <ns4:sub>R</ns4:sub> )of the α <ns4:sub>1</ns4:sub> 1.2 size forms, extensive systematic immunoblotting of brain tissue as well as full length and C-terminally truncated α <ns4:sub>1</ns4:sub> 1.2 expressed in HEK293 cells was conducted using six different region–specific antibodies against α <ns4:sub>1</ns4:sub> 1.2. </ns4:p> <ns4:p> <ns4:bold>Results</ns4:bold> : The full length form of α <ns4:sub>1</ns4:sub> 1.2 migrated, as expected, with an apparent M <ns4:sub>R</ns4:sub> of ~250 kDa. A shorter form of comparable prevalence with an apparent M <ns4:sub>R</ns4:sub> of ~210 kDa could only be detected in immunoblots probed with antibodies recognizing α <ns4:sub>1</ns4:sub> 1.2 at an epitope 400 or more residues upstream of the C-terminus. </ns4:p> <ns4:p> <ns4:bold>Conclusions</ns4:bold> : The main two size forms of α <ns4:sub>1</ns4:sub> 1.2 are the full length form and a shorter form, which lacks ~350 distal C-terminal residues. Midchannel cleavage as suggested by Michailidis <ns4:italic>et al</ns4:italic> . (2014) is at best minimal in brain tissue. </ns4:p>