Abstract
This study compares the role of electrostatics in the binding process between microtubules and two dynein microtubule-binding domains (MTBDs): cytoplasmic and axonemal. These two dyneins are distinctively different in terms of their functionalities: cytoplasmic dynein is processive, while axonemal dynein is involved in beating. In both cases, the binding requires frequent association/disassociation between the microtubule and MTBD, and involves highly negatively charged microtubules, including non-structured C-terminal domains (E-hooks), and an MTBD interface that is positively charged. This indicates that electrostatics play an important role in the association process. Here, we show that the cytoplasmic MTBD binds electrostatically tighter to microtubules than to the axonemal MTBD, but the axonemal MTBD experiences interactions with microtubule E-hooks at longer distances compared with the cytoplasmic MTBD. This allows the axonemal MTBD to be weakly bound to the microtubule, while at the same time acting onto the microtubule via the flexible E-hooks, even at MTBD–microtubule distances of 45 Å. In part, this is due to the charge distribution of MTBDs: in the cytoplasmic MTBD, the positive charges are concentrated at the binding interface with the microtubule, while in the axonemal MTBD, they are more distributed over the entire structure, allowing E-hooks to interact at longer distances. The dissimilarities of electrostatics in the cases of axonemal and cytoplasmic MTBDs were found not to result in a difference in conformational dynamics on MTBDs, while causing differences in the conformational states of E-hooks. The E-hooks’ conformations in the presence of the axonemal MTBD were less restricted than in the presence of the cytoplasmic MTBD. In parallel with the differences, the common effect was found that the structural fluctuations of MTBDs decrease as either the number of contacts with E-hooks increases or the distance to the microtubule decreases.
Highlights
Cytoplasmic dynein is one of the three different families of motor proteins moving toward the minus end of cytoskeleton filaments to do diverse activities, such as transport cargos including proteins, organelles, and mRNAs in eukaryotic cells [1,2,3,4]
Since axonemal microtubule-binding domains (MTBDs) carries a positive net charge while cytoplasmic MTBD is neutral between the axonemal and cytoplasmic MTBDs, and the microtubule, are shown in Figure 2
The electrostatic field between the axonemal and cytoplasmic MTBDs, and the microtubule, are shown in Figure 2
Summary
Cytoplasmic dynein is one of the three different families of motor proteins moving toward the minus end of cytoskeleton filaments (microtubules) to do diverse activities, such as transport cargos including proteins, organelles, and mRNAs in eukaryotic cells [1,2,3,4]. On the other hand, is non-processive, and it causes the sliding of microtubules [5,6]. Cytoplasmic and axonemal dynein share some structural similarities [7], their functions within the cell are different [8,9,10]. Cytoplasmic dyneins are composed of two identical chains, stepping processively along microtubules. In cilia and flagella, the dyneins are involved in the beating of cilia and flagella. In both cases, the dyneins interact with microtubules via a microtubule-binding domain (MTBD), which adopts different conformations due to the signal provided by the linker and ATP (Adenosine triphosphate) -binding domain [11,12]. It has been shown that a change in registry (α and β) between two antiparallel coiled coil helices, called the stalk [13], alters the microtubule binding affinity of cytoplasmic MTBD [11,14]; this effect is small for axonemal MTBD [7]
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