Sfi1

Sfi1 is a conserved coiled-coil protein that participates in the duplication of spindle pole bodies in yeast and centrosomes in animal cells. In budding yeast (Saccharomyces cerevisiae) Sfi1 localizes to the spindle pole body (SPB) and is required for SPB duplication. In vertebrates, Sfi1 associates with centrosomes and binds centrin proteins, suggesting a conserved role in centrosome maintenance during cell division.

Function: Sfi1 forms a structural scaffold, often described as a bridge, that links the old and new SPBs during duplication and provides a platform for the assembly of duplication components. Its interaction with centrin (Cdc31 in yeast; CETN2 in humans) is key to this process; centrin-binding repeats within Sfi1 mediate these contacts.

Structure and localization: Sfi1 proteins are large, predominantly coiled-coil, and can assemble into extended filaments. The localization is cell-cycle regulated, with enrichment at SPBs or centrosomes during duplication phases and dispersal afterward.

Significance: Disruption of Sfi1 function leads to defects in SPB/centrosome duplication, abnormal spindle formation, and chromosome missegregation. The protein is conserved across fungal and animal lineages, underscoring its fundamental role in cell division. In humans, aberrant centrosome duplication is linked to cancer and developmental disorders, making Sfi1 a focus of studies on centrosome biology.

Research outlook: Ongoing studies examine the detailed molecular interactions between Sfi1, centrin, and other centrosomal components, aiming to clarify the assembly dynamics of the duplication scaffold.