科研之友
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摘要
Voltage-gated calcium channels are multiprotein complexes that regulate calcium influx and are important contributors to cardiac excitability and contractility. The auxiliary beta-subunit (CaVB) binds a conserved domain (the alpha-interaction domain (AID)) of the pore-forming Ca-V alpha(1) subunit to modulate channel gating properties and promote cell surface trafficking. Recently, members of the RGK family of small GTPases (Rem, Rem2, Rad, Gem/Kir) have been identified as novel contributors to the regulation of L-type calcium channel activity. Here, we describe the Rem-association domain within Ca-V beta(2a). The Rem interaction module is located in a similar to 130-residue region within the highly conserved guanylate kinase domain that also directs AID binding. Importantly, Ca-V beta mutants were identified that lost the ability to bind AID but retained their association with Rem, indicating that the AID and Rem association sites of Ca-V beta(2a) are structurally distinct. In vitro binding studies indicate that the affinity of Rem for Ca-V beta(2a) interaction is lower than that of AID for Ca-V beta(2a). Furthermore, in vitro binding studies indicate that Rem association does not inhibit the interaction of Ca-V beta(2a) with AID. Instead, CaV beta can simultaneously associate with both Rem and Ca-V alpha(1)-AID. Previous studies had suggested that RGK proteins may regulate Ca2+ channel activity by blocking the association of Ca-V beta subunits with Ca-V alpha(1) to inhibit plasma membrane trafficking. However, surface biotinylation studies in HIT-T15 cells indicate that Rem can acutely modulate channel function without decreasing the density of L-type channels at the plasma membrane. Together these data suggest that Rem-dependent Ca2+ channel modulation involves formation of a Rem(.)Ca(V)beta(.)AID regulatory complex without the need to disrupt Ca-V alpha Ca-.(1)V beta association or alter Ca-V alpha(1) expression at the plasma membrane.
- 出版日期2006-8-18
