Subclassification of the RBCC/TRIM Superfamily Reveals a Novel Motif Necessary for Microtubule Binding

Abstract

The biological significance of RBCC (N-terminal RING finger/Bbox/coiled coil) proteins is increasingly being appreciated following demonstrated roles in disease pathogenesis, tumorigenesis, and retroviral protective activity. Found in all multicellular eukaryotes, RBCC proteins are involved in a vast array of intracellular functions; but as a general rule, they appear to function as part of large protein complexes and possess ubiquitin-protein isopeptide ligase activity. Those members characterized to date have diverse C-terminal domain compositions and equally diverse subcellular localizations and functions. Using a bioinformatics approach, we have identified some new RBCC proteins that help define a subfamily that shares an identical domain arrangement (MID1, MID2, TRIM9, TNL, TRIM36, and TRIFIC). Significantly, we show that all analyzed members of this subfamily associate with the microtubule cytoskeleton, suggesting that subcellular compartmentalization is determined by the unique domain architecture, which may in turn reflect basic functional similarities. We also report a new motif called the COS box, which is found within these proteins, the MURF family, and a distantly related non-RBCC microtubule-binding protein. Notably, we demonstrate that mutations in the COS box abolish microtubule binding ability, whereas its incorporation into a nonmicrotubule-binding RBCC protein redirects it to microtubule structures. Further bioinformatics investigation permitted subclassification of the entire human RBCC complement into nine subfamilies based on their varied C-terminal domain compositions. This classification schema may aid the understanding of the molecular function of members of each subgroup and their potential involvement in both basic cellular processes and human disease.Members of the RBCC (N-terminal RING finger/B-box/coiled coil) or TRIM (tripartite motif) family of proteins perform a diverse array of cellular roles, yet are believed to share some functional properties: 1) act as a scaffold for the assembly of larger multiprotein complexes and 2) possess RING-dependent ubiquitin ligase activity (1, 2). The RBCC domain can be found in isolation or in combination with a variety of other C-terminal domains, including the NHL (NCL-1/HT2A/LIN-41 repeat), immunoglobulin, MATH (meprin and tumor necrosis factor receptor-associated factor homology), B30.2-like/RFP (Ret finger protein)/SPRY (SplA and ryanodine receptor) (the largest subgroup in humans), ARF (ADP-ribosylation factor), PHD (plant homeodomain finger), and BROMO domains (1, 2). As a family of proteins, their biological significance is perhaps best highlighted by the growing number that have a demonstrated role in disease pathogenesis, including immunological and developmental disorders, tumorigenesis, and retroviral protective activity (3-7).We have previously identified and characterized two RBCC proteins, MID1 and its closely related homolog, MID2. MID1 and MID2 contain a B30.2-like domain at their C terminus and a single fibronectin type III (FN3...

Antibodies to TRIM46 are associated with paraneoplastic neurological syndromes

“…TRIM36 is a family member that is highly similar to TRIM4613 but does not localize to axonal microtubules and is not recognized by the patients’ antibodies. By swapping domains of TRIM46 with the corresponding regions of TRIM36, we were able to identify the specific domains to which the anti‐TRIM46 antibodies are directed.…”

“…The TRIM46 and TRIM36 DNA clones were kindly provided by Dr. T Cox 13. Expression constructs and chimeric constructs were generated in‐house by PCR as described in Ref.…”

TRIM5α Cytoplasmic Bodies Are Highly Dynamic Structures

“…We have demonstrated that this motility involves the microtubule cytoskeleton (Figure 4), demonstrating that TRIM5␣ cytoplasmic bodies exhibit active translocation within the cell. Other studies have identified a COS motif present in a subset of TRIM proteins that mediates microtubule binding (Short and Cox, 2006). Although TRIM5␣ does not possess this motif, it is nevertheless able to interact with the microtubule network to facilitate its intracellular transport.…”

Hypospadias associated with hypertelorism, the mildest phenotype of Opitz syndrome

“…14 The C-terminus consists of a COS box, fibronectin type 3 domain and a B30.2 domain (PRY+SPRY). 16 As an E3 ubiquitin ligase, MID1 has been shown to regulate phosphatase 2A catalytic subunit degradation. 15,17 In addition, MID1 is involved in the formation of multiprotein complex serving as anchor points and associated with microtubuli.…”