Membrane targeting of the EF-hand containing calcium-sensing proteins CaBP7 and CaBP8

Abstract

The CaBP family of EF-hand containing small Ca2+-binding proteins have recently emerged as important regulators of multiple targets essential to normal neuronal function in the mammalian central nervous system. Of particular interest are CaBP7 and CaBP8, abundantly expressed brain proteins that exhibit the greatest sequence divergence from other family members. In this study, we have analysed their sub-cellular localisations in a model neuronal (Neuro2A) cell line and show that both proteins exhibit a membrane distribution distinct from the other CaBPs and consistent with localisation to the trans-Golgi network (TGN). Furthermore, we show that their localisation to the TGN critically depends upon an unusual predicted C-terminal transmembrane domain that if deleted or disrupted has dramatic consequences for protein targeting. CaBP7 and 8, therefore, possess a targeting mechanism that is unique amongst the CaBPs that may contribute to differential functional Ca2+-sensing by these family members.

Calneurons provide a calcium threshold for trans -Golgi network to plasma membrane trafficking

“…Calneurons do not harbor a Nmyristoylation motif and therefore the question arises as to how they can be tethered to the Golgi. While this study was under review it was reported that calneurons contain in their C terminus a transmembrane domain that might be responsible for Golgi targeting of the overexpressed protein (30). It remains, however, elusive how this transmembrane domain can provide a Golgi membrane anchor.…”

The Diversity of Calcium Sensor Proteins in the Regulation of Neuronal Function

“…A major difference compared with calmodulin is the ability of CaBP 1 and 2 and calneurons 1 and 2 to target to specific cellular membranes (McCue et al 2009). CaBP 1 and 2 are amino-terminally myristoylated, which permits localization to the plasma membrane and Golgi apparatus (Haeseleer et al 2000;Haynes et al 2004).…”

“…The precise amino-terminal sequence to which the myristoyl group is attached is also important in the targeting of these two proteins, as exemplified by the long and short splice isoforms generated from their genes, which show subtle differences in their localization. CaBP1-Long localizes predominantly to the Golgi and also displays some cytosolic localization, whereas CaBP1-Short localizes most prominently to the plasma membrane and to Golgi structures (Haeseleer et al 2000;McCue et al 2009). Alternative splicing of the CaBP1 gene generates athird protein product, caldendrin (Seidenbecher et al 1998).…”

“…Like CaBP1 and CaBP2, calneurons 1 and 2 localize to internal membranes that colabel with Golgi-specific markers and also to vesicular structures (McCue et al 2009;Mikhaylova et al 2009). Calneurons 1 and 2 do not possess an amino-terminal myristoylation motif and differ from the rest of the CaBP family because of a 38-amino acid extension at their carboxyl terminus.…”

“…Cite this article as Cold Spring Harb Perspect Biol 2010;2:a004085 and directly localizes calneurons 1 and 2 to membranes particularly of the trans-Golgi network (McCue et al 2009). …”