Summary: Two unrelated proteins aggregate in UHT milk over a period of months to form amyloid fibrils.
Source: Australian National University.
A new study on UHT milk is helping scientists to better understand Alzheimer’s, Parkinson’s and type 2 diabetes, opening the door to improved treatments for these age-related diseases.
About 500 million people worldwide suffer from these diseases, which cause millions of deaths each year.
Co-lead researcher, ANU Professor John Carver, said that two unrelated proteins aggregate in UHT milk over a period of months to form clusters called amyloid fibrils, which cause the milk to transform from a liquid into a gel.
He said the same type of protein clusters are found in plaque deposits in cases of Alzheimer’s and Parkinson’s.
“Parkinson’s, dementia and type 2 diabetes are big problems for the ageing population in Australia and many other countries around the world,” said Professor Carver from the ANU Research School of Chemistry.
“Our interest in milk proteins led to a discovery of the reason for this gelling phenomenon occurring in aged UHT milk.”
“The research does not suggest UHT milk can cause these age-related diseases.”
Professor Carver said milk proteins changed structurally when heated briefly to around 140 degrees to produce UHT milk, causing the gelling phenomenon with long-term storage.
He said normal pasteurised milk did not form amyloid fibrils.
ANU worked with CSIRO, University of Wollongong and international researchers on the study, which is published in the journal Small.
Source: Will Wright – Australian National University
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Original Research: Abstract for “Coaggregation of κ-Casein and β-Lactoglobulin Produces Morphologically Distinct Amyloid Fibrils” by Jared K. Raynes, Li Day, Pauline Crepin, Mathew H. Horrocks, and John A. Carver in Small. Published online February 1 2017 doi:10.1002/smll.201603591
Coaggregation of κ-Casein and β-Lactoglobulin Produces Morphologically Distinct Amyloid Fibrils
The unfolding, misfolding, and aggregation of proteins lead to a variety of structural species. One form is the amyloid fibril, a highly aligned, stable, nanofibrillar structure composed of β-sheets running perpendicular to the fibril axis. β-Lactoglobulin (β-Lg) and κ-casein (κ-CN) are two milk proteins that not only individually form amyloid fibrillar aggregates, but can also coaggregate under environmental stress conditions such as elevated temperature. The aggregation between β-Lg and κ-CN is proposed to proceed via disulfide bond formation leading to amorphous aggregates, although the exact mechanism is not known. Herein, using a range of biophysical techniques, it is shown that β-Lg and κ-CN coaggregate to form morphologically distinct co-amyloid fibrillar structures, a phenomenon previously limited to protein isoforms from different species or different peptide sequences from an individual protein. A new mechanism of aggregation is proposed whereby β-Lg and κ-CN not only form disulfide-linked aggregates, but also amyloid fibrillar coaggregates. The coaggregation of two structurally unrelated proteins into cofibrils suggests that the mechanism can be a generic feature of protein aggregation as long as the prerequisites for sequence similarity are met.
“Coaggregation of κ-Casein and β-Lactoglobulin Produces Morphologically Distinct Amyloid Fibrils” by Jared K. Raynes, Li Day, Pauline Crepin, Mathew H. Horrocks, and John A. Carver in Small. Published online February 1 2017 doi:10.1002/smll.201603591