Evolutionary reconstruction of the retromer complex and its function in Trypanosoma brucei

Abstract

SummaryIntracellular trafficking and protein sorting are mediated by various protein complexes, with the retromer complex being primarily involved in retrograde traffic from the endosome or lysosome to the Golgi complex. Here, comparative genomics, cell biology and phylogenetics were used to probe the early evolution of retromer and its function. Retromer subunits Vps26, Vps29 and Vps35 are near universal, and, by inference, the complex was an ancient feature of eukaryotic cells. Surprisingly, we found DSCR3, a Vps26 paralogue in humans associated with Down's syndrome, in at least four eukaryotic supergroups, implying a more ancient origin than previously suspected. By contrast, retromer cargo proteins showed considerable interlineage variability, with lineage-specific and broadly conserved examples found. Vps10 trafficking probably represents an ancestral role for the complex. Vps5, the BAR-domaincontaining membrane-deformation subunit, was found in diverse eukaryotes, including in the divergent eukaryote Trypanosoma brucei, where it is the first example of a BAR-domain protein. To determine functional conservation, an initial characterisation of retromer was performed in T. brucei; the endosomal localisation and its role in endosomal targeting are conserved. Therefore retromer is identified as a further feature of the sophisticated intracellular trafficking machinery of the last eukaryotic common ancestor, with BAR domains representing a possible third independent mechanism of membrane-deformation arising in early eukaryotes.

Rab28 function in trypanosomes: interactions with retromer and ESCRT pathways

“…Disruption of sphingolipid biosynthesis through inhibition of serine palmitoyltransferase has a similar effect on the Golgi complex, but the effect is relatively mild (Fridberg et al, 2008). However, disruption of Golgi morphology upon depletion of T. brucei Rab28 parallels Vps26 knockdown in mammalian cells and trypanosomes (Seaman, 2004;Koumandou et al, 2011). The absence of conventional retromer cargo from trypanosomes means that direct investigation of retromer function is difficult, but the complex probably mediates similar functions in both systems (Koumandou et al, 2011).…”

“…However, disruption of Golgi morphology upon depletion of T. brucei Rab28 parallels Vps26 knockdown in mammalian cells and trypanosomes (Seaman, 2004;Koumandou et al, 2011). The absence of conventional retromer cargo from trypanosomes means that direct investigation of retromer function is difficult, but the complex probably mediates similar functions in both systems (Koumandou et al, 2011). Gross morphological aberrations at the Golgi complex potentially result through depletion of SNAREs or other factors required for correct homotypic fusion due to defective retrieval from late endosomes, i.e.…”

“…T. brucei possesses orthologues of the cargo-recognition retromer subcomplex (Vps26, Vps29 and Vps35) and one sorting nexin (Vps5), suggesting conserved function (Koumandou et al, 2011).…”

RME-8 coordinates the WASH complex with the retromer SNX-BAR dimer to control endosomal tubulation

“…An analysis of the conservation of RME-8 (Koumandou et al, 2013) concluded that it is well conserved but with numerous secondary losses. Retromer was first identified in yeast and is ubiquitously conserved (Seaman et al, 1997;Seaman et al, 1998;Koumandou et al, 2011). The WASH complex, although widely conserved and likely to be ancient in origin (Derivery and Gautreau, 2010), is not conserved in yeast -which is also true for RME-8.…”

Evolutionary variations of VPS29, and their implications for the heteropentameric model of retromer

“…Given that retromer is conserved across all eukaryotes, 5 it is perhaps surprising that studies of retromer in mammalian cells revealed that (unlike S. cerevisiae) the complex is not a stable heteropentamer. The cargo-selective trimer is a stable complex, as is the SNX-BAR dimer but the two subcomplexes associate only transiently.…”