A dual Golgi- and mitochondria-localised Ala25Ser precursor cystatin C: an additional tool for characterising intracellular mis-localisation leading to increased AMD susceptibility.
An artificial mutant Ala25Ser precursor cystatin C was created to help elucidate the cause of intracellular mis-localisation of the biochemically related variant B (Ala25Thr) precursor cystatin C to the mitochondria. Homozygotes of variant B precursor cystatin C were reported to carry an increased susceptibility to developing the exudative form of AMD. Ala25Ser precursor cystatin C shows a dual distribution to the Golgi apparatus and to the mitochondria. This localisation is thus intermediary between that of wild-type cystatin C (targeted to ER/Golgi compartment) and that of variant B precursor cystatin C. Furthermore, the level of secretion of Ala25Ser cystatin C by RPE cells is intermediary between wild type and variant B cystatin C. Ala25Ser precursor cystatin C thus represents a biochemical intermediate between the wild type and the AMD-associated cystatin C and as such, is a novel tool for the investigation of the mechanism of intracellular mis-localisation of variant B cystatin C. Our findings further support the hypothesis that substitution of the alanine residue in the penultimate position of precursor cystatin C signal sequence with a less hydrophobic amino acid residue, such as threonine (as in variant B cystatin C) or serine is sufficient to impair the intracellular trafficking and processing of the protein.
Ratnayaka
Arjuna
A
Paraoan
Luminita
L
Spiller
Dave G
DG
Hiscott
Paul
P
Nelson
Glyn
G
White
Michael R H
MR
Grierson
Ian
I
D055316:Cystatin C; D015891:Cystatins / Q000235:genetics*; D020022:Genetic Predisposition to Disease; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D008268:Macular Degeneration / Q000235:genetics*; D008928:Mitochondria / Q000378:metabolism
C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins