Proteomics: milk composition

Introduction

The project is part of Dutch Milk Genomic Initiative (MGI). In MGI, milk from 2000 cows were measured, variation in the milk composition are observed.

The composition of milk, and its variability, depends on the synthesis of the major components of milk (fat, protein, lactose) in the udder. In these synthesis pathways, there are many minor proteins involved, such as enzymes, transporters and regulators. The variation in quality or quantity of these minor proteins may influence the synthesis pathways and lead to the variation of milk composition.  

Proteomics technique have been widely used nowadays to study the proteins. By using this, the proteins can be identified , quantified and also the modification and interaction can be found. The proteomics technique have been also applied widely to milk  research in the last few years. But the quantitation of milk proteins were not  well studied.

Aim

Using proteomic techniques to quantify the minor proteins and enzymes in the milk, try to find explanations for the variation in milk composition.

Research

In this study, LC-ESI-Obitrap-MS/MS was used to identify and quantify the minor proteins in different milk fractions—milk fat globule membrane proteins and milk serum proteins. For the quantitation of proteins, dimethyl labelling was used. It was a relative quantification method. The digested peptides were labelled with isotopomeric dimethyl labels. The labeled samples are mixed and simultaneously analyzed by LC-MS whereby the mass difference of the dimethyl labels is used to compare the peptide abundance in the different samples.

A new method called FASP were used in the project for proteins pretreatments before MS running in stead of using 1D or 2D gels, which were widely used in proteomics studies nowadays. The FASP overcame the disadvantages of the gels that they were not suitable for quantitation. Around 160 proteins were found in milk fat globule membrane and 100 proteins in milk serum in our research. 15 proteins of them were related to fat synthesis, and 14 of them were related to protein synthesis. Two of them were related to lactose synthesis. There were also 13 transporters identified.

Future research

Try to find the answers of these three questions:

1. Which proteins and enzymes related to milk production can be identified and quantified using the current state of proteomics techniques?
2. Can proteins and enzymes which are related to milk production be used to explain the variation in milk composition?
3. Can the information found by analyzing the proteome be used to find genetic markers for variation in milk composition?