Temperature-induced structural changes of apo-lactoferrin and their functional implications: a molecular dynamics simulation study

Lactoferrin (Lf) is an iron-binding glycoprotein present in secretory fluids from human and bovine sources. Sequence alignment was employed to identify a region on the C-lobe of Lf capable of binding to bacterial cell surfaces, followed by all-atom explicit solvent molecular dynamics simulations to study the conformational changes of Lf after exposure to three processing temperatures: pasteurisation (72 degrees C), spray drying (90 degrees C) and ultra-high temperature (UHT) (127 degrees C). Below 90 degrees C, the simulations indicate relatively minor changes in overall protein structure. At UHT conditions (127 degrees C), however, marked disruptions to protein structure were found as demonstrated by a substantial decrease in protein dimensions due to collapse in the inter-lobe region. There was also a marked increase in residue fluctuations in several regions of known functional importance, including antibacterial, iron-binding, and putative membrane binding regions, the latter of which is stabilised by a triplet of hydrophobic residues comprised of Leu446, Trp448 and Leu451 at low temperature, but which are disrupted under UHT conditions. A unique network analysis confirmed these results as demonstrated by large clusters of residues with increased dynamical correlation in the N-terminal lobe.