Lecture 1 Flashcards
Is glucose a reducing or non-reducing sugar and why?
Glucose is a reducing sugar because it has a free aldehyde group that can act as a reducing agent and become oxidised itself
Give one reason why glucose being a reducing sugar may cause oxidative cellular damage?
Increase in reactive oxygen species due to increased polyol pathway flux
Why does increased polyol pathway flux cause oxidative cellular damage?
The aldose reductase enzyme that oxidises the glucose intracellularly to its respective alcohol using NADPH as a cofactor leads to reduction in available NADH.
NADH is used to regenerate glutathione (GSH) which is an important scavenger of ROS
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2996922/
In which tissues is aldose reductase found?
nerve, retina, lens, glomerulus and vascular cells
Why are tissues such as nerve, retina, lens, glomerulus and vascular cells more at risk of damage from hyperglycaemia?
The GLUT transporters that move glucose intracellularly from the blood are insulin-independent so moves straight into cell and accumulates.
What are the three main types of diabetes mellitus and what are the main features of each type?
Type 1 - autoimmune destruction of pancreatic islets of Langerhans beta cells so insulin not produced
Type 2 - acquired insulin resistance
Gestational diabetes - first detected in pregnancy
Which cells secrete insulin?
Beta cells of islets of langerhans in pancreas
Which cells perceive insulin?
muscle cells and hepatocytes (liver)
What is the overall effect of insulin?
decreases blood glucose level
Which cells produce glucagon?
alpha cells of islets of langerhans in pancreas
Which cells perceive glucagon?
most hepatocytes (liver)
What is the overall effect of glucagon?
Increase blood glucose level
Describe the structure of the Sarcoma Homology 2 (SH2) domain
antiparallel beta-sheet flanked by two alpha helices
What feature is recognised by SH2 domains?
pY (phosphotyrosine residue)
How do modular binding domains convey specificity?
All proteins in the same domain family recognise the same feature but each individual domain only recognises this feature in a given motif.
Name four modular binding domain families
- Sarcoma Homology 2 (SH2)
- Sarcoma Homology 3 (SH3)
- Phosphotyrosine Binding (PTB) domain
- Pleckstrin Homology (PH) domain
Give the definition of a protein domain
a conserved part of a given protein sequence that forms a compact three-dimensional structure that is independently stable and folded, and may evolve, function, and exist independently.
What is the amino acid sequence of the SH2 domain that binds the pY residue and why is it important?
FLVR
- the positively charged R (arginine) will be able to coordinate the negatively charged pY
Which part of the SH2 domain affects specificity?
The C-terminal flanking sequence (variability in the primary sequence of the substrate)
What feature is recognised by SH3 domains?
Proline rich PXXP cores (aromatic proline residues)
Why do SH3 domains exhibit avidity?
binds with a weaker affinity so multiple SH3 domains bind to increase the association constant
What feature is recognised by PH domains?
PIPs (phospholipids) - binds phosphate of phosphoinositides
What is the structure of the SH3 domain?
5 anti-parallel beta strands in two perpendicular beta sheets
What feature is recognised by the PTB domains?
pY (Phosphotyrosine)
What is the motif recognised by PTB domains?
NPXpY
What increases binding affinity and specificity of the PTB domains?
N-terminal sequences flanking the recognised motif and pY
What is the structure of the PTB domain?
2 orthogonal beta-sheets with a c-terminal amiphipathic alpha-helix capping one end of the beta sandwich
Why are the N-terminal flanking sequences of the PTB binding peptide important?
increases binding affinity and specificity
forms an additional anti-parallel beta-strand to the second beta sheet of the domain
What controls the specificity of recognition of different phosphoinositide’s by the PH domains?
The location of the phosphate and the number of phosphates
What is the structure of the PH domain?
Beta-barrel of two antiparallel beta-sheets and amphipathic alpha-helix
