The protein (3144 aa) encoded by the IT15 gene that has variable numbers of polyglutamine repeats in Huntington's disease. The IT15 gene is widely expressed and required for normal development. The mutant Htt protein forms insoluble nuclear aggregates which may be responsible for neuronal cell death in the disease although a range of other effects have been suggested. The polyglutamine repeats (44 in the commonest form of the disease) increase the interaction of huntingtin with a membrane-bound huntingtin-associated protein-1 (HAP-1, 671 aa) which is expressed more abundantly in the hypothalamus than in other brain regions. HAP1 may function as an adaptor protein mediating interaction with cytoskeletal and motor proteins and the HAP1-huntingtin complex may play a role in vesicle trafficking. Huntingtin-interacting protein (HIP-1, 1037 aa) is membrane-associated and has similarity to cytoskeleton proteins; it interacts with clathrin heavy chain and α-adaptins A and C, suggesting it may be involved in endocytotic vesicle activity. HIP-1 binds to the HIP1 protein interactor (HIPPI) to form a pro-apoptotic heterodimer. Huntingtin-interacting protein-12 (HIP-1 related protein, 1068 aa) has some regions of similarity with HIP-1 with which it interacts. Other huntingtin-interacting proteins include the glycolytic enzyme GAPD, pacsin1, and the ubiquitin-conjugating enzyme E2–25K (HIP2).
Subjects: Medicine and Health.