Abstract
Rab2 requires atypical protein kinase C iota/lambda (aPKC iota/lambda) to promote vesicle formation from vesicular tubular clusters (VTCs). The Rab2-generated vesicles are enriched in recycling proteins suggesting that the carriers are retrograde-directed and retrieve transport machinery back to the endoplasmic reticulum. These vesicles also contained the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). We have previously established that GAPDH is required for membrane transport between the endoplasmic reticulum and the Golgi complex. Moreover, GAPDH is phosphorylated by aPKC iota/lambda and binds to the aPKC iota/lambda regulatory domain. In this study, we employed a combination of in vivo and in vitro assays and determined that GAPDH also interacts with Rab2. The site of GAPDH interaction was mapped to Rab2 residues 20-50. In addition to its glycolytic function, GAPDH has multiple intracellular roles. However, the function of GAPDH in the early secretory pathway is unknown. One possibility is that GAPDH ultimately provides energy in the form of ATP. To determine whether GAPDH catalytic activity was critical for transport in the early secretory pathway, a conservative substitution was made at Cys-149 located at the active site, and the mutant was biochemically characterized in a battery of assays. Although GAPDH (C149G) has no catalytic activity, Rab2 recruited the mutant protein to membranes in a quantitative binding assay. GAPDH (C149G) is phosphorylated by aPKC iota/lambda and binds directly to Rab2 when evaluated in an overlay binding assay. Importantly, VSV-G transport between the ER and Golgi complex is restored when an in vitro trafficking assay is performed with GAPDH-depleted cytosol and GAPDH (C149G). These data suggest that GAPDH imparts a unique function necessary for membrane trafficking from VTCs that does not require GAPDH glycolytic activity.
Highlights
Since Rab2 interacts with aPKC/ and aPKC/ associates with glyceraldehyde-3phosphate dehydrogenase (GAPDH), it seemed plausible that Rab2 might directly bind GAPDH
To determine whether GAPDH catalytic activity was critical for transport in the early secretory pathway, a conservative substitution was made at Cys-149 located at the active site, and the mutant was biochemically characterized in a battery of assays
To address the question whether GAPDH catalytic activity was critical for transport in the early secretory pathway, a conservative substitution was made at the invariant residue (Cys-149) located at the active site
Summary
Since Rab2 interacts with aPKC/ and aPKC/ associates with GAPDH, it seemed plausible that Rab2 might directly bind GAPDH. GAPDH (C149G) has no catalytic activity, Rab2 recruited the mutant protein to membranes in a quantitative binding assay. We found using a combination of in vivo and in vitro assays that Rab2 associates with GAPDH suggesting that Rab2, aPKC/, and GAPDH form a complex on VTCs. GAPDH binds to residues 20 –50 in Rab2.
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