Hinge-loop mutation can be used to control 3D domain swapping and amyloidogenesis of human cystatin C
[CYTC_HUMAN] Defects in CST3 are the cause of amyloidosis type 6 (AMYL6) [MIM:105150]; also known as hereditary cerebral hemorrhage with amyloidosis (HCHWA), cerebral amyloid angiopathy (CAA) or cerebroarterial amyloidosis Icelandic type. AMYL6 is a hereditary generalized amyloidosis due to cystatin C amyloid deposition. Cystatin C amyloid accumulates in the walls of arteries, arterioles, and sometimes capillaries and veins of the brain, and in various organs including lymphoid tissue, spleen, salivary glands, and seminal vesicles. Amyloid deposition in the cerebral vessels results in cerebral amyloid angiopathy, cerebral hemorrhage and premature stroke. Cystatin C levels in the cerebrospinal fluid are abnormally low.  Genetic variations in CST3 are associated with age-related macular degeneration type 11 (ARMD11) [MIM:611953]. ARMD is a multifactorial eye disease and the most common cause of irreversible vision loss in the developed world. In most patients, the disease is manifest as ophthalmoscopically visible yellowish accumulations of protein and lipid that lie beneath the retinal pigment epithelium and within an elastin-containing structure known as Bruch membrane.
[CYTC_HUMAN] As an inhibitor of cysteine proteinases, this protein is thought to serve an important physiological role as a local regulator of this enzyme activity.
Publication Abstract from PubMed
Cystatins are natural inhibitors of cysteine proteases, enzymes that are widely distributed in animals, plants, and microorganisms. Human cystatin C (hCC) has been also recognized as an aggregating protein directly involved in the formation of pathological amyloid fibrils, and these amyloidogenic properties greatly increase in a naturally occurring L68Q hCC variant. For a long time only dimeric structure of wild-type hCC has been known. The dimer is created through 3D domain swapping process, in which two parts of the cystatin structure become separated from each other and next exchanged between two molecules. Important role in the domain swapping plays the L1 loop, which connects the exchanging segments and, upon dimerization, transforms from a beta-turn into a part of a long beta-strand. In the very recently published first monomeric structure of human cystatin C (hCC-stab1), dimerization was abrogated due to clasping of the beta-strands from the swapping domains by an engineered disulfide bridge. We have designed and constructed another mutated cystatin C with the smallest possible structural intervention, that is a single-point mutation replacing hydrophobic V57 from the L1 loop by polar asparagine, known as a stabilizer of a beta-turn motif. V57N hCC mutant occurred to be stable in its monomeric form and crystallized as a monomer, revealing typical cystatin fold with a five-stranded antiparallel beta-sheet wrapped around an alpha-helix. Here we report a 2.04A resolution crystal structure of V57N hCC and discuss the architecture of the protein in comparison to chicken cystatin, hCC-stab1 and dimeric hCC.
Hinge-loop mutation can be used to control 3D domain swapping and amyloidogenesis of human cystatin C.,Orlikowska M, Jankowska E, Kolodziejczyk R, Jaskolski M, Szymanska A J Struct Biol. 2010 Nov 11. PMID:21074623
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.