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Myoglobin is an α-helical globular protein containing two highly conserved tryptophanyl residues at positions 7 and 14 in the N-terminal region. The double W/F replacement renders apomyoglobin highly susceptible to aggregation and amyloid-like fibril formation under physiological conditions. In this work we analyze the early stage of W7FW14F apomyoglobin aggregation following the time dependence of the process by far-UV CD, Fourier-transform infrared (FTIR) spectroscopy, and heme-binding properties. The results show that the aggregation of W7FW14F apomyoglobin starts from a native-like globin state able to bind the prosthetic group with spectroscopic properties similar to those observed for wild-type apoprotein. Nevertheless, it rapidly aggregates, forming amyloid fibrils. However, when the prosthetic group is added before the beginning of aggregation, amyloid fibrillization is inhibited, although the aggregation process is not prevented. Moreover, the apomyoglobin aggregates formed in these conditions are not cytotoxic differently from what is observed for all amyloidogenic proteins. These results open new insights into the relationship between the structure adopted by the protein into the aggregates and their ability to trigger the impairment of cell viability. [ABSTRACT FROM AUTHOR]

Abstract: In protein deposition disorders, a normally soluble protein is deposited as insoluble aggregates, referred to as amyloid. The intrinsic effects of specific mutations on the rates of protein aggregation and amyloid formation of unfolded polypeptide chains can be correlated with changes in hydrophobicity, propensity to convert α-helical to β sheet conformation and charge. In this paper, we report the aggregation rates of buffalo, horse and bovine apomyoglobins. The experimental values were compared with the theoretical ones evaluated considering the amino acid differences among the sequences. Our results show that the mutations which play critical roles in the rate-determining step of apomyoglobin aggregation are those located within the N-terminal region of the molecule. [Copyright &y& Elsevier]