The interplay between calcium and the in vitro lectin and chaperone activities of calreticulin.
The ER resident protein calreticulin fulfills at least two important roles. It works as a chaperone preventing Golgi exit of non-native protein species and enhancing protein folding efficiency in either N-glycan-dependent, lectin chaperone, or classical chaperone, N-glycan-independent, modes and is one of the main calcium buffers in the cell. This last feature is independent from the lectin chaperone properties of the protein as this last activity is also observed in a CRT fragment lacking calcium buffer capacity. Here we study the interplay between calcium and the lectin and chaperone activities of CRT. The affinity of CRT for monoglucosylated glycans measured in solution by equilibrium dialysis and fluorescence anisotropy was not affected by the absence of calcium. Binding of CRT to monoglucosylated neoglycoproteins displaying either native or molten globule-like conformations was also independent of calcium concentration. Moreover, calcium and monoglucosylated glycans stabilized the CRT structure in an apparent additive, independent manner when the protein was subjected to thermal or urea-induced denaturation. In addition, the ability of CRT to decrease the level of aggregation of a chemically denatured monoglucosylated and nonglycosylated protein was also independent of calcium level.
Conte
Ianina L
IL
Laboratory of Glycobiology, Fundación Instituto Leloir, Av. Patricias Argentinas 435, Buenos Aires C1405BWE, Argentina.
Keith
Natasha
N
Gutiérrez-Gonzalez
Clara
C
Parodi
Armando J
AJ
Caramelo
Julio J
JJ
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D037282:Calreticulin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002850:Chromatography, Gel; D002942:Circular Dichroism; D019281:Dimerization; D005454:Fluorescence Polarization; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism; D037102:Lectins / Q000737:chemistry* / Q000378:metabolism; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011489:Protein Denaturation / Q000187:drug effects; D017434:Protein Structure, Tertiary; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013696:Temperature; D013997:Time Factors; D014508:Urea / Q000494:pharmacology
D037282:Calreticulin; D006023:Glycoproteins; D037102:Lectins; D018832:Molecular Chaperones; D009844:Oligosaccharides; D010455:Peptides; D010940:Plant Proteins; D011134:Polysaccharides; D011994:Recombinant Proteins; C093336:chymotrypsin inhibitor 2; D014508:Urea; D002118:Calcium