Comments on “Structural basis for microtubule binding and release by dynein”.

I evaluated the following article for F1000 Prime:

Redwine WB, Hernández-López R, Zou S, Huang J, Reck-Peterson SL, Leschziner AE. (2012) Structural basis for microtubule binding and release by dynein. Science 337, 1532-6. PMID: 22997337 DOI: 10.1126/science.1224151

My comments build on those from Terrence Frey (San Diego State University) which provide a nice description of the structural data in this paper.

I entirely agree with the thoughts of Terrence Frey here. The concept of a sub-maximal dynein constrained by virtue of an intramolecular salt bridge is a very intriguing one. The possibility that this provides dynein-1 with a greater “dynamic range” seems quite likely. I very much like the proposed explanation that cytoplasmic dynein-2, which is involved in long range unidirectional transport in cilia and flagella, is not constrained in this way because it lacks the possibility to form such a salt bridge. This provides a nice explanation for the need to maintain two distinct cytoplasmic dynein heavy chains.

 

Dynein alone?

I evaluated the following article for F1000:

Dynein light chain 1 and a spindle-associated adaptor promote dynein asymmetry and spindle orientation.
AK Dunsch, D Hammond, J Lloyd, L Schermelleh, U Gruneberg and FA Barr J Cell Biol. 2012 Sep 17; 198(6): 1039-54
PMID: 22965910 DOI: 10.1083/jcb.201202112

The thing that fascinates me the most about this is the possibility that dynein containing light chain-1 acts without dynactin…..hence the crap title for the post.

This paper is highly intriguing from a dynein motor perspective as it strongly suggests that, in mitosis, the binding of dynein light chain 1 (DYNLL1) and the major dynein regulator dynactin are mutually exclusive. The work details very clearly how the adaptor proteins CHICA and HMMR target dynein to the mitotic spindle. This serves to control spindle positioning in cells, at least in part through promoting dynein asymmetry. It will be fascinating to determine whether DYNLL1 and dynactin can bind to dynein at the same time in interphase cells; this would of course have major implications for those studying dynein and dynactin function.

A Golgi anchor for dynein

I started my lab in 2001 with the aim of defining the mechanisms that link endomembranes, particularly those operating in membrane trafficking between the ER and Golgi, to the microtubule cytoskeleton. This month in Developmental Cell, Adam Linstedt’s lab published the following paper:

Golgin160 Recruits the Dynein Motor to Position the Golgi Apparatus.

Smita Yadav, Manojkumar A. Puthenveedu, Adam D. Linstedt

Developmental Cell

Volume 23, Issue 1, 17 July 2012, Pages 153–165 http://dx.doi.org/10.1016/j.devcel.2012.05.023,

I must say that I am very impressed with this paper – it is precisely the one that I wish we had published from my lab. Of course there is much more to do but this is a definitive answer to a question. Nicely done.

Yadav and colleagues set out by defining a role for golgin160 (also known as golgin-160 in the literature) in minus end directed movement of Golgi membranes using siRNA depletion. They also showed that dynein is no longer recruited to Golgi membranes in the absence of golgin160 using an antibody against the dynein light chain Tctex-1. This is no mean feat and immuno-detection of dynein is notoriously difficult and unreliable. They also showed that golgin160 interacts through its own C-terminal coiled coil domain with the dynein intermediate chain subunit. This interaction is direct with a relatively weak (~1 micromolar) affinity.

Golgin160 is a peripheral membrane protein which of course leaves open the question of how it is recruited to membrane to subsequently drive recruitment of dynein. The answer turned out to be Arf1, a small GTP binding protein that operates in ER-to-Golgi transport, primarily to recruit the COPI complex. COPI drives retrograde trafficking from the Golgi to the ER. The N-terminal domain of Golgin160 (i.e. not that which binds dynein) binds preferentially to active GTP-bound Arf1. Consistent with this hierarchical mechanism, golgin160 is not required for the recruitment of GBF1, the main Arf1-activator at this point in the cell¹.

Finally the authors show that Golgin160 dissociates from Golgi membranes during mitosis. This is perhaps not surprising given that it is well known that COPI-dependent membrane traffic is largely arrested during mitosis^{2, 3}. However, it does provide a nice mechanism to drive Golgi disassembly during mitosis. Inhibition (or at least down-regulation) of Arf1 activation would lead to a loss of golgin160 from membranes which would in turn lead to a failure to recruit dynein. This would mean reduced minus end motility and consequently a failure to maintain the Golgi as a juxtanuclear organelle.

These data are very clear and convincing. There are also some nice nuances for aficionados. Importantly the fact that this process relies on Arf1 activation at the start suggests that golgin160 might indeed be a more universal membrane anchor for dynein operating at the Golgi itself as well as in ER-to-Golgi trafficking. My own lab showed previously that the COPII coat⁴ can recruit dynactin, a key accessory factor to dynein that is also required for ER-to-Golgi transport⁵. However, the COPII complex is only involved very locally at ER exit sites⁶ and so another factor must be involved as early as the ER-Golgi intermediate compartment (ERGIC). This factor looks likely to be golgin160. In agreement with this, Yadav et al find that dynactin can be identified in complex with golgin160 and dynein. Whether there is an additional membrane anchor for dynactin, or whether this role is performed by spectrin for example⁷, remains to be defined. Golgin160 is also cleaved during apoptosis by caspase-2⁸ so these new data suggest an obvious mechanism by which this would cause rapid dissociation of the Golgi.

Other questions do remain. How does this golgin160 pathway relate to what we know about the role of Cdc42 and the COPI coat in the recruitment of dynein^{9, 10}.

References:

1.             Szul T, et al. Traffic (2005);6:374-385.

2.             Altan-Bonnet N, et al. Mol Biol Cell (2006);17:990-1005.

3.             Altan-Bonnet N, et al. Proc Natl Acad Sci U S A (2003);100:13314-13319.

4.             Jensen D, Schekman R. J Cell Sci (2011);124:1-4.

5.             Watson P, et al. Nat Cell Biol (2005);7:48-55.

6.             Budnik A, Stephens DJ. FEBS Lett (2009);583:3796-3803.

7.             Holleran EA, et al. J Cell Biol (1996);135:1815-1829.

8.             Mancini M, et al. The Journal of cell biology (2000);149:603-612.

9.             Hehnly H, et al. Traffic (2010);11:1067-1078.

10.          Chen JL, et al. J Cell Biol (2005);169:383-389.

Evaluated article: Binding of Dynein Intermediate Chain 2 to Paxillin controls Focal adhesion dynamics and migration.

I evaluated the following article for Faculty of 1000. The original evaluation is available at:

http://f1000.com/715347821

C Rosse,K Boeckeler,M Linch,S Radtke,D Frith,K Barnouin,AS Morsi,M Hafezparast,M Howell,PJ Parker
Binding of Dynein Intermediate Chain 2 to Paxillin controls Focal adhesion dynamics and migration.
J Cell Sci 2012 PMID: 22553211 DOI: 10.1242/jcs.089557

This article nicely defines a role for dynein phosphorylation in cell migration through interaction with the focal adhesion protein paxillin. The authors show that dynein is phosphorylated during cell migration, using an unbiased proteomic approach. The dynein intermediate chain is phosphorylated in serine-84 by atypical protein kinase C isoforms, as shown by mutagenesis and inhibitor studies. The data show that dynein has a role in controlling the stability of focal adhesions and suggest a model in which phosphorylation of dynein on its intermediate chain subunit decreases its affinity for paxillin. While the work leaves many questions unanswered, it provides a nice piece in the puzzle of how dynein regulates focal adhesion dynamics.