Background
Apolipoprotein A-I (apoA-I) protects against atherosclerosis and participates in the removal of excess cellular cholesterol from peripheral organs. Several naturally occurring apoA-I mutations are associated with familial systemic amyloidosis, with deposition of amyloid aggregates in peripheral organs, resulting in multiple organ failure. Systematic studies on naturally occurring variants are needed to delineate their roles and involvement in pathogenesis.
Methods
We performed a comparative structure–function analysis of five naturally occurring apoA-I variants and the wild-type protein. Circular dichroism, Fourier-transform infrared spectroscopy, thioflavin T and congo red fluorescence assays, thermal, chemical, and proteolytic stability assays, and 1,2-Dimyristoyl-
sn
-glycero-3-phosphocholine clearance analyses were used to assess the effects of mutations on the structure, function, stability, aggregation, and proteolytic susceptibility of the proteins to explore the mechanisms underlying amyloidosis and hypercholesterolemia.
Results
We observed structural changes in the mutants independent of fibril formation, suggesting the influence of the surrounding environment. The mutants were involved in aggregate formation to varying degree; L170P, R173P, and V156E showed an increased propensity to aggregate under different physiological conditions. β sheet formation indicates that L170P and R173P participate in amyloid formation. Compared to WT, V156E and L170P exhibited higher capacity for lipid clearance.
Conclusions
The selected point mutations, including those outside the hot spot regions of apoA-I structure, perturb the physiochemical and conformational behavior of the protein, influencing its function.
General significance
The study provides insights into the structure–function relationships of naturally occurring apoA-I variants outside the hot spot mutation sites.
Hyperglycemia is a poorly controlled diabetic condition, affects about 70 percent of people all round the world. In the year 2015, about 41.5 crore people were diabetic and is expected to reach around 64.3 crore by the year 2040. Cardiovascular diseases (CVDs) are considered as one of the major risk factors that cause more than half of the death of diabetic patients and promote related comorbidities. Atherosclerosis and amyloidosis are the prime rudimentary cause associated with CVDs. Apolipoprotein A-I (ApoA-I) of high-density lipoprotein (HDL) have protective action against CVDs, participate in reverse cholesterol transport (RCT) mechanism and lipid metabolism, but gets easily glycated under prolonged hyperglycemic aura i.e. glycation. ApoA-I have a potent role in maintenance of glucose level, providing a compelling link between diabetes and CVDs. Increased protein glycation in people with diabetes promote atherosclerosis which might play possible role in promotion of protein aggregation by altering the protein structure and its confirmation. Here, we intend to investigate the mechanistic behavior of ApoA-Iunder the menace of glycation and its impact on ApoA-I structure and function that possibly link with aggregation or amyloidosis.
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