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I'm going over some of my notes, and I have written down that motor proteins with + cytoskeletal directionality have a reversed schematic representation relative to - directed motor proteins. Then I have this sort of image drawn. I just want to clarify it, since I don't remember this part of lecture at all.


Schematic representations

  • Kinesin: N terminal - |Head||Coils||Tail| - C terminal

  • Dynein: N terminal - |Tail||Coils||Head|| - C terminal

Does this look right?

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  • $\begingroup$ I don't understand your question. Both schematics are the same, just written in reverse. The 5' end of an mRNA always codes for the N-terminal end of a protein. Perhaps your asking which protein domain (head or tail) occurs at the N-terminal end in each type of motor? $\endgroup$ – canadianer Apr 5 '15 at 5:31
  • $\begingroup$ Sorry! It's been a long day. I fixed it to what it should've been. Now their motor domains are at the opposite termini. $\endgroup$ – Drowsy Apr 5 '15 at 7:01
  • $\begingroup$ "The direction in which cargo is transported is dependent in part upon the position of the motor domain, which can be located N-terminally (N-kinesins), C-terminally (C-kinesins) or internally (M-kinesins). In general, kinesins with N-terminal motor domains move their cargo towards the plus ends of microtubules located at the cell periphery, while kinesins with C-terminal motor domains move cargo towards the minus ends of microtubules located at the nucleus." Source $\endgroup$ – CKM Apr 6 '15 at 22:51
  • $\begingroup$ @drowsy Feel free to roll back my edits if my understanding is inaccurate. $\endgroup$ – CKM Apr 7 '15 at 21:15
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No. DNA, and RNA have a polarity in the orientation of their sugar-phosphate backbones, based on the numbering of the carbon atoms in the sugar rings. So, for example, we say that the sequence of this RNA is being read from the 5' to the 3' end, which indicates that the first nucleotide is exposing the hydroxyl at the 5’ carbon on its sugar ring. At the other end of the linear polynucleotide the sugar is exposing the hydroxyl on its 3’ carbon of the sugar ring.

All mRNAs are translated in the 5’ to 3’ direction and all proteins are synthesized from the amino terminus to the carboxylate terminus, because the peptide bonds in the protein also have a directional polarity.

You appear to have mislabeled the N and C termini of Dynein in your diagram. Perhaps the lecture was about the domain structure of these two motor proteins? And the point might have been that they each have three equivalent domains but in one case the part we call the head is synthesized first and in the other case the tail is synthesized first(?).

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  • $\begingroup$ I did. Thanks for catching that. But thanks for your response. It makes sense. Basically one is translated motor first and one is translated tail first, right? $\endgroup$ – Drowsy Apr 5 '15 at 7:02
  • $\begingroup$ I don't know if that is true, because it has been a long time since I thought about motor proteins, but yes, that is what your diagram shows must be the case. I would go so far as to say that these two very large ATP-ases that Carry cargo along microtubules share related structural domains but since the proteins are modular you can mix and match the modules in different combinations $\endgroup$ – mdperry Apr 5 '15 at 13:01
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So, as I pointed out in comments, and requoting:

"The direction in which cargo is transported is dependent in part upon the position of the motor domain, which can be located N-terminally (N-kinesins), C-terminally (C-kinesins) or internally (M-kinesins). In general, kinesins with N-terminal motor domains move their cargo towards the plus ends of microtubules located at the cell periphery, while kinesins with C-terminal motor domains move cargo towards the minus ends of microtubules located at the nucleus."

And that was a short excerpt from Jennifer McDowall on Interpro. And then just surveying kinesins from the mouse genome,

enter image description here

Source: Kinesin superfamily motor proteins and intracellular transport

In terms of dyneins, however, I believe they're all (-)-directed motor proteins with the following general structure,

enter image description here

Source: The 2.8 Å crystal structure of the dynein motor domain

Keep in mind these representations are always expressed N-terminal (left) to C-terminal (right). So while your model for dyneins is correct, for kinesins this depends on the location of the motor domain.

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