1. Intro: PTMs Flashcards
What are the different types of PTMs?
Glycosylation, phosphorylation, disulfide bonding.
What affects the extent and variety of modifications of a protein? What do these modifications result in?
- The individual protein.
- Regulatory mechanisms in the cell.
- Environmental factors.
They result in the dynamic nature of proteins and proteomics.
What are the different properties that can affect protein properties and what type of PTMs are involved in each of these properties?
Biochemical, chemical and physical properties.
1. Biochemical properties: disulfide bonding results in dimer and multimer formation, which results in binding capabilities.
2. Chemical properties: phosphorylation and glycosylation results in the change in pI and charge of a protein.
3. Physical properties: glycosylation can alter the molecular weight of a protein.
What is glycosylation?
It is the adding of sugar chains (moieties) to a polypeptide, resulting in glycoproteins.
What is the purpose of glycosylation?
It increases solubility, bioactivity, and circulation time in the cell. They also result in the heterogeneity of proteins due to the different extent of glycosylation.
What are N and O glycans?
N glycans are sugar chains that are attached to asparagine residues. O glycans are sugar chains that are attached to serine or threonine residues.
What is the mechanism behind N linked glycans?
In the cytosol the sugar chain attaches to a lipid precursor to form a sugar-lipid complex. It then flips itself into the lumen of the endoplasmic reticulum. More sugar chains get added to complete the core oligosaccharide, and the complex then attaches to a nascent growing polypeptide chain. The sugar chain then gets trimmed while the polypeptide gets folded. The glycoprotein then gets sent to the Golgi apparatus where further modifications of the protein occur and the capping of the branches of the oligosaccharide with sialic acid and fucose occurs.
What does neuraminidase do for viruses?
The virus and the cell and produces virions the virions leave the cell, but get stuck on the cell membrane due to sialic acid interactions between the cellular and viral receptors. Neuraminidase cleaves the sialic acid between the receptors, allowing for virions to leave.
What do neuraminidase inhibitors do?
They mimic sialic acid by binding to the active site of neuraminidase, preventing viral release
What is phosphorylation?
It is the adding of phosphate groups to proteins to form phosphoproteins.
What does phosphorylation result in?
It changes the activity of proteins reversibly.
In which amino acid residues does phosphorylation occur in?
Phosphate groups, get attached to serine, threonine and tyrosine.
Where does disulfide bonding occur?
Cysteine residues
What is the mechanism behind disulfide bonding?
Redox reactions occur inter- and intra- molecularly, catalyzed by thiol oxidoreductase, resulting in dimer and multimer formations and the folding of proteins.
What is the general process of proteomic analysis?
- Sample preparation.
- Sample separation.
- Visualization.
- Comparative analysis.
- Mass spectrometry.
