Tim21

Tim21, also known as TIMM21 in humans, is a mitochondrial inner membrane protein that functions as a subunit of the TIM23 translocase complex. It is implicated in the import of nuclear-encoded proteins into mitochondria, a process that relies on the TIM23 complex to move preproteins across the inner membrane.

In most organisms studied, Tim21 is a small, hydrophobic protein with at least one transmembrane segment, anchoring it in the inner mitochondrial membrane. The regions of Tim21 face both the matrix and the intermembrane space, consistent with a role in coordinating protein translocation through the TIM23 machinery. Tim21 associates with core TIM23 components and modulates the activity and efficiency of preprotein import, contributing to the sorting decisions that determine whether a precursor is delivered to the matrix or integrated into the inner membrane.

Localization and evolution: Tim21 is localized to the inner mitochondrial membrane and is a component of the conserved TIM23 translocase pathway across eukaryotes. The gene is conserved and is named TIM21 in yeast (Tim21p) and TIMM21 in mammals, reflecting its preserved role in mitochondrial protein import.

Clinical and research relevance: Defects in mitochondrial protein import can contribute to cellular dysfunction, but there is no widely established disease directly attributed to Tim21 deficiency alone. Tim21 remains a subject of ongoing research to delineate its precise interactions within the TIM23 complex and its impact on import routing under different cellular conditions.

See also: TIM23 complex; mitochondrial protein import; Tim23; Tim17; Tim50.