Is There Any Correlation Between Thermodynamic Stability And Amyloidogenicity? Studies With WT And Variants Of The Immunoglobulin Light Chain.
CARVALHO K.M.P 1; MORGADO L.B 1; LIMA F.S 1; FREITAS M.S 1; YAUNER L.P 2; BECERRIL B 2; and FOGUEL D 1.
1-INSTITUTO DE BIOQUÍMICA MÉDICA, CENTRO DE CIÊNCIAS DA SAÚDE, UNIVERSIDADE FEDERAL DO RIO DE JANEIRO, BRAZIL.;
2-DEPARTMENT OF MOLECULAR MEDICINE AND BIOPROCESSES, INSTITUTE OF BIOTECHNOLOGY, NATIONAL AUTONOMUS UNIVERSITY OF MEXICO, CUERNAVACA, MEXICO.
Amyloidosis is a vast group of diseases defined by the presence of insoluble protein deposits in tissues. Primary amyloidosis (AL) is characterized by the deposition in vital organs and tissues of aggregates composed predominantly of the variable region (VL) of monoclonal immunoglobulin light chains (Bence Jones protein). The -λ6 subgroup has been found to be preferentially associated with this disease. It has been observed that the LC protein from patients with AL accumulates more than 10-12 mutations simultaneously along its sequence, what could be associated with the disease. In the present study we constructed several point mutants aiming to mimic the effect of all these mutations. The positions deeply investigated were 2 and 25 which are located in loop L1. The spatial orientation of Arg25 side chain seems to be determined by planar interaction between its guanidyl group and the Phe2 group, being the last residue typical of l VI proteins. LC has a trp residue located at position 35. This position lies very close to a disulphide bridge which quenches completely trp emission. Thus in the native state LC has no trp fluorescence emission. However, denatured by high pressure, as used here, the trp emission increases around 3-6 times depending on the variant. In the present study we compared the thermodynamic stability among wt and variants of the LC, namely, F2S, F2W, H8S, R25G, F2P, P7S, Wil and Jto. The experiments were performed at 370C and 250C . From the pressure denaturation curve we were able to calculate all the thermodynamic parameter (∆G and ∆V) of the folding of the LC. From our data we could identify three distinct families that present low, medium and high stabilities. These data will be presented and discussed. We also compared the amyloidogenic properties of all these variants related to the wt protein. Our aim is to construct a map where the thermodynamic and amyloidogenicity of each variant will be compared to see if there is any correlation.
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