An unpredicted aggregation-critical region of the actin-polymerizing protein TRIOBP-1/Tara, determined by elucidation of its domain structure

Abstract

Aggregation of specific proteins in the brains of patients with chronic mental illness as a result of disruptions in proteostasis is an emerging theme in the study of schizophrenia in particular. Proteins including DISC1 (disrupted in schizophrenia 1) and dysbindin-1B are found in insoluble forms within brain homogenates from such patients. We recently identified TRIOBP-1 (Trio-binding protein 1, also known as Tara) to be another such protein through an epitope discovery and proteomics approach by comparing post-mortem brain material from schizophrenia patients and control individuals. We hypothesized that this was likely to occur as a result of a specific subcellular process and that it, therefore, should be possible to identify a region of the TRIOBP-1 protein that is essential for its aggregation to occur. Here, we probe the domain organization of TRIOBP-1, finding it to possess two distinct coiled-coil domains: the central and C-terminal domains. The central domain inhibits the depolymerization of F-actin and is also responsible for oligomerization of TRIOBP-1. Along with an N-terminal pleckstrin homology domain, the central domain affects neurite outgrowth. In neuroblastoma cells it was found that the aggregation propensity of TRIOBP-1 arises from its central domain, with a short "linker" region narrowed to within amino acids 324-348, between its first two coiled coils, as essential for the formation of TRIOBP-1 aggregates. TRIOBP-1 aggregation, therefore, appears to occur through one or more specific cellular mechanisms, which therefore have the potential to be of physiological relevance for the biological process underlying the development of chronic mental illness.

Localization and functional consequences of a direct interaction between TRIOBP-1 and hERG proteins in the heart

“…These vesicular aggregates were also visible in all cells evaluated for AP and current properties, and did not appear to affect cell viability. Other studies on TRIOBP-1 also show that aggregates form upon overexpression of TRIOBP-1 without an effect on viability (Bradshaw et al, 2014(Bradshaw et al, , 2017. We conclude that reduction of I Kr current density upon TRIOBP-1 overexpression is primarily attributable to the co-sequestration of hERG protein in internal vesicular or vacuolar structures.…”

TRIOBP-5 sculpts stereocilia rootlets and stiffens supporting cells enabling hearing

“…Exons 18,19,21,23, and 24 encode residues common to TRIOBP-1 and TRIOBP-5 that are predicted to form 5 coiled-coil domains ( Figure 1A and Supplemental Figure 8). Some of these coiled-coils allow TRIOBP-1 to oligomerize (14). To gain additional insight into the domain architecture and possible dimerization of mouse TRIOBP-5, we performed an amino acid sequence analysis to identify putative coiled-coil domains using COILS (41).…”

“…To gain additional insight into the domain architecture and possible dimerization of mouse TRIOBP-5, we performed an amino acid sequence analysis to identify putative coiled-coil domains using COILS (41). Five coiled-coil domains were identified at residues 1669-1689, 1719-1754, 1792-1819, 1890-1917, and 1928-1962 of mouse TRIOBP-5 (NCBI ABB59557.2), equivalent to the coiled-coil domains described for human TRIOBP-5 (14). Next, we generated an in silico template-based structural model (see Methods and Supplemental Figure 8) in order to analyze the 3D arrangement of these coiled-coil domains.…”

“…TRIO is a regulator of cytoskeletal remodeling, cell growth, and motility that activates Rho GTPases (9)(10)(11)(12)(13). TRIOBP-1 has 5 predicted coiled-coil domains and a pleckstrin homology domain (PH) ( Figure 1A), binds and stabilizes actin filaments, and is required for embryonic viability (8,(14)(15)(16)(17). TRIOBP-4 is predicted to be a disordered protein that binds F-actin by its R1-repeat motifs (18) and has no amino acid sequence in common with TRIOBP-1, while TRIOBP-5 includes the entire amino acid sequence of TRIOBP-4, most of the sequence of TRIOBP-1, and more ( Figure 1A).…”

“…TRIOBP-4 is predicted to be a disordered protein that binds F-actin by its R1-repeat motifs (18) and has no amino acid sequence in common with TRIOBP-1, while TRIOBP-5 includes the entire amino acid sequence of TRIOBP-4, most of the sequence of TRIOBP-1, and more ( Figure 1A). Thus, TRIOBP-5 contains all of the actin-binding repeat motifs of TRIOBP-4 (18) and additional ones (14). TRIOBP-4 and TRIOBP-5 are expressed in human and mouse retina, brain, and inner ear (5,6,8).…”