• Question from:Sanjukta

Does depolymerisation take place at the minus end of microtubule?








Wikipedia says that

Dynamic instability refers to the coexistence of assembly and disassembly at the 'ends' of a microtubule.

but Karp's Cell Biology, 7th edition says

Dynamic instability is an inherent property of microtubule itself, more specifically, of the plus end of the microtubule.

I was of the opinion that the GTP bound to the minus end does not hydrolyse and so no depolymerisation take place at the minus end.

But again from The Cell: A Molecular Approach. 2nd edition I found that

treadmilling is a dynamic behavior in which tubulin molecules bound to GDP are continually lost from the minus end and replaced by the addition of tubulin molecules bound to GTP to the plus end of the same microtubule.

The concept I have developed so far is completely shattered by this treadmilling thing. Can you explain,

i) Whether GTP remains attached to the minus end?

ii) Whether depolymerisation occurs at the minus end?

iii) If depolymerisation does not occur, then is treadmilling a special condition?

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Most polymerisation and depolymerisation happens at the plus end where GTP bound molecules are added and removed by hydrolysis of GTP to GDP.
At the minus end are GTP bound molecules. Depolymerisation can occur when the GTP is hydrolysed to GDP (the GTP stabilises the microtubule).
Polymerisation at the plus end and deploymerisation at the plus and minus ends can all occur at different rates but when polymerisation at the plus end and deploymerisation at the minus end occur at the same rate treadmilling occurs.