Abstract
The TRIM family of proteins is distinguished by its tripartite motif (TRIM). Typically, TRIM proteins contain a RING finger domain, one or two B-box domains, a coiled-coil domain and the more variable C-terminal domains. TRIM16 does not have a RING domain but does harbour two B-box domains. Here we showed that TRIM16 homodimerized through its coiled-coil domain and heterodimerized with other TRIM family members; TRIM24, Promyelocytic leukaemia (PML) protein and Midline-1 (MID1). Although, TRIM16 has no classic RING domain, three-dimensional modelling of TRIM16 suggested that its B-box domains adopts RING-like folds leading to the hypothesis that TRIM16 acts as an ubiquitin ligase. Consistent with this hypothesis, we demonstrated that TRIM16, devoid of a classical RING domain had auto-polyubiquitination activity and acted as an E3 ubiquitin ligase in vivo and in vitro assays. Thus via its unique structure, TRIM16 possesses both heterodimerization function with other TRIM proteins and also has E3 ubiquitin ligase activity.
Highlights
The tripartite motif (TRIM)/Ring finger, B box, coiled-coil (RBCC) family of proteins are defined by the presence of the tripartite motif
We show that TRIM16 can homodimerize through its coiled-coil domain and bind to other TRIM proteins; Midline-1 (MID-1/TRIM18), Promyelocytic leukemia protein (PML/TRIM19) and TRIM24 (TIF-1a)
TRIM16 Homodimerizes via Its Coiled-Coil Domain In the large and evolutionary conserved TRIM family, specific domains tend to operate as functional units
Summary
The tripartite motif (TRIM)/Ring finger, B box, coiled-coil (RBCC) family of proteins are defined by the presence of the tripartite motif. The full-length TRIM16 and 5 deletion constructs were used to probe for the role of various domains in protein function (Figure 1A).
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