Lecture 5 - Cytoskeletal PTMs

Question 1

Where do Tubulin sequence variations/PTMs occur?

Answer 1

Clustered in the C-terminal tubulin tails (CTTs)

Question 2

Give 3 Examples of CTT Post-Translational Modifications?

Answer 2

• Polyglycylation - addition of Glycine residues to side chains of E residues in a/B-CTTs
• Detyrosination - removal of C-terminal Y residues on a-CTTs (may also remove other residues)
• Polyglutamylation - addition of E residues to a/B-CTTs, targeting many internal sites

Question 3

(i) Are there any examples of MT Lumenal PTMs?

(ii) What is their effect?

Answer 3

(i) Acetylation of K40 of a-Tubulin by aTAT1

(ii) Weaken lateral interactions between protofilaments, making MTs more flexible and therefore more stable/long-lived

Question 4

What is the purpose of C-terminal tubulin tails (CTTs)

Answer 4

Involved in the regulation of processivity and velocity of MT motor proteins (Kinesins, Dyneins)

Question 5

How could CTTs regulate motor activity in terms of:
(i) Possible Mechanisms
(ii) Possible Impacts

Answer 5

(i) Possible Mechanisms:
* Alteration of Electrostatic Interactions
* Alteration of Specific Docking Interactions

(ii) Possible Impacts:
* Regulation of Motor protein transport by marking favoured tracks
* Regulation of Balance of Movement between different motor types

Question 6

What is the Importance of Tubulin PTMs in Axonemal MTs?

Answer 6

Polyglycylation/Polyglutamylation - impact formation and function of cilia, with lack of PTMs leading to impaired mucocillary clearance

Question 7

How does absence of Axonemal PTMs impact mucocillary clearance?

(2 Points)

Answer 7

• Axonemes of WT-mouse tracheal cilia have intrinsic curvature that supports beating asymmetry
• This beating asymmetry is dependent on polyglutamylation, hence its absence leads to loss of beating asymmetry and mucus accumulation

Question 8

Define the Tubulin Code Hypothesis

Answer 8

Specific Tubulin isotypes/PTMs confer specific biochemical activities to MTs, influencing dynamics and the transport activity along them

Question 9

Give Two Examples of Disorders associated with Tubulin PTMs

Answer 9

1. Cardiomyopathies - importance of load-bearing MTs during cardiac contraction
2. Male Infertility - polyglutamylation is very important to axonemal beating, therefore affects sperm flagella

Question 10

How do N-terminal modifications (e.g., Acetylation, Arginylation) alter Actin Filament Properties?

Answer 10

Known to Affect Polymerisation Kinetics, with:
* Acetylation-KD - Increasing Filament formation, decreasing G/F-actin ratio
* Arginylation-KD - Leading to filament aggregation, impairing cell movement/spreading