Search

The many progressive achievements in knowledge about the structure and function of the nephron – the kidney’s main morpho-functional unit – have always been influenced by philosophical theories, which for a long time have swung between vitalism and mechanism. From Galen’s first imaginative vitalistic hypothesis, the scientific thought about the kidney’s structure/function gradually moved to the iatro-mechanistic view promoted by Borelli, Bellini and Malpighi, to then meet Bowman’s bright vitalistic-based theory. But Bowman’s theory was rather soon replaced by novel yet still mechanistic theories proposed first by Ludwig and then Starling. Ludwig based his scientific approach to knowledge of renal function upon physics and chemistry; Starling eventually developed a ‘colloid-osmotic’ theory.

Myoglobin is an alpha-helical globular protein that contains two highly conserved tryptophan residues located at positions 7 and 14 in the N-terminal region of the protein. Replacement of both indole residues with phenylalanine residues, i.e. W7F/W14F, results in the expression of an unstable, not correctly folded protein that does not bind the prosthetic group. Here we report data (Congo red and thioflavine T binding assay, birefringence, and electron microscopy) showing that the double Trp/Phe replacements render apomyoglobin molecules highly susceptible to aggregation and amyloid-like fibril formation under physiological conditions in which most of the wild-type protein is in the native state. In refolding experiments, like the wild-type protein, the W7F/W14F apomyoglobin mutant formed a soluble, partially folded helical state between pH 2.0 and pH 4.0. A pH increase from 4.0 to 7.0 restored the native structure only in the case of the wild-type protein and determined aggregation of W7F/W14F. The circular dichroism spectrum recorded immediately after neutralization showed that the polypeptide consists mainly of beta-structures. In conclusion, under physiological pH conditions, some mutations that affect folding may cause protein aggregation and the formation of amyloid-like fibrils.