[ACTN4_HUMAN] Defects in ACTN4 are the cause of focal segmental glomerulosclerosis type 1 (FSGS1) [MIM:603278]. A renal pathology defined by the presence of segmental sclerosis in glomeruli and resulting in proteinuria, reduced glomerular filtration rate and edema. Renal insufficiency often progresses to end-stage renal disease, a highly morbid state requiring either dialysis therapy or kidney transplantation.
[ACTN4_HUMAN] F-actin cross-linking protein which is thought to anchor actin to a variety of intracellular structures. This is a bundling protein. Probably involved in vesicular trafficking via its association with the CART complex. The CART complex is necessary for efficient transferrin receptor recycling but not for EGFR degradation.
Mutations in alpha-actinin-4 have been linked to familial focal segmental glomerulosclerosis (FSGS), a common renal disorder in humans, and produce an apparent increase in the actin-binding affinity of alpha-actinin-4 in vitro. One of the mutations, in particular, Lys255Glu, falls in the middle of the actin-binding interface of the actin-binding domain (ABD). The ABD consists of tandem calponin homology (CH) domains (CH1 and CH2). The crystal structures of most ABDs display a compact conformation, characterized by extensive inter-CH interactions. However, the conformation of F-actin-bound ABDs is unsettled. Some electron microscopy studies find that the compact conformation is preserved upon binding to F-actin, whereas other studies suggest that the CHs separate and the ABD becomes extended. The Lys255Glu mutation in CH2 is significant in this regard since it removes a crucial inter-CH interaction with Trp147 of CH1, thought to stabilize the compact conformation. Together, the increased actin-binding affinity and the removal of this important inter-CH contact suggested that the Lys255Glu mutation might facilitate the transition toward the open ABD conformation proposed by some of the electron microscopy studies. However, the crystal structure of the ABD of alpha-actinin-4 Lys255Glu mutant described here displays the canonical compact conformation. Furthermore, the sedimentation coefficients by analytical ultracentrifugation of wild-type and FSGS mutant ABDs (Lys255Glu, Ser262Pro, and Thr259Ile) are nearly identical (2.50+/-0.03 S) and are in good agreement with the theoretical value calculated from the crystal structure (2.382 S), implying that the compact conformation is retained in solution. The absence of a structural change suggests that the compact ABD conformation observed in the majority of the structures is highly stable and is preserved in solution, even in FSGS mutant ABDs.
Crystal structure of the actin-binding domain of alpha-actinin-4 Lys255Glu mutant implicated in focal segmental glomerulosclerosis.,Lee SH, Weins A, Hayes DB, Pollak MR, Dominguez R J Mol Biol. 2008 Feb 15;376(2):317-24. Epub 2007 Dec 4. PMID:18164029
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
↑ Kaplan JM, Kim SH, North KN, Rennke H, Correia LA, Tong HQ, Mathis BJ, Rodriguez-Perez JC, Allen PG, Beggs AH, Pollak MR. Mutations in ACTN4, encoding alpha-actinin-4, cause familial focal segmental glomerulosclerosis. Nat Genet. 2000 Mar;24(3):251-6. PMID:10700177 doi:10.1038/73456
↑ Lee SH, Weins A, Hayes DB, Pollak MR, Dominguez R. Crystal structure of the actin-binding domain of alpha-actinin-4 Lys255Glu mutant implicated in focal segmental glomerulosclerosis. J Mol Biol. 2008 Feb 15;376(2):317-24. Epub 2007 Dec 4. PMID:18164029 doi:10.1016/j.jmb.2007.11.084