Length of KASH Domains Affect Linc Complex Functions

Abstract

The linker of the nucleoskeleton and cytoskeleton (LINC) complexes are composed of inner nuclear membrane Sad1/UNC-84 (SUN, and outer nuclear membrane Klarsicht/ANC-1/SYNE homology (KASH) proteins. LINC complexes span the physical barrier of the nuclear envelope and regulate the physical connection between the interior of the nucleus and the cytoplasm during various cellular functions. The large cytoplasmic domains of KASH proteins bind to various elements of the cytoskeleton, whereas their 10-30 amino acid KASH domains reside in the perinuclear space (PNS) where they bind to SUN proteins. Interestingly, different KASH domain proteins can independently bind to the same SUN protein to mediate distinct cellular functions. For example, in mammals the SUN protein SUN1 can transiently associate with KASH5 in the PNS to mediate meiotic chromosome movement. Alternatively, SUN1 can bind to Nesprin1/2 to mediate nuclear movement. Similarly, in Caenorhabditis elegans (C. elegans) SUN protein UNC-84 transiently binds to KASH protein UNC-83 in embryonic hypodermal cells to mediate nuclear migration. Later, the same SUN protein UNC-84 independently binds to a different KASH protein ANC-1 to anchor of the nucleus in place for several days. In this work, we combined in vivo C. elegans genetics and in silico molecular dynamics simulations to explore the role of KASH domain length on the function of the SUN-KASH complex and its response to mechanical forces. Our results imply that longer KASH domains can withstand and transfer higher forces across the SUN-KASH complex. Additionally, our results suggest that longer KASH domains can interact with the membrane through a conserved membrane proximal EEDY domain that is unique to longer KASH domains. Finally, we show that swapping the KASH domains of ANC-1 and UNC-83, or shortening the KASH domain of ANC-1, both result in a nuclear anchorage defect in C. elegans.