Talk:Myosin

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Is there anyone here who know something about the scallop myosin?

-The Scallop Myosin has a completely different regulation as mammalian myosin, calcium enhances its ATPase whereas for most other myosins it can cause disassociation the calmodulins resulting in lower force production or extend its ATPase cycle to near infinity, resulting in essentially a myosin anchor (myosin 1b does this). - Myosin guy

I think approximate concentration of myosin need to be mentioned in the article. Light&Truth 04:43, 11 April 2006 (UTC)

I arrived at this myosin site after discovering the Harvard illustrations shown in the address. Those animations are so informative and beautiful, they should be cited here. JK Wolf http://multimedia.mcb.harvard.edu/

It currently mentions that type IV moves to the +ve end of microtubules, then goes on to state that type VI is the only type which does so. Maybe the second statement should be removed? JM —Preceding unsigned comment added by 58.214.233.2 (talk) 14:39, 16 May 2010 (UTC)

Myosin II subtypes[edit]

Does anyone think it's relevant to describe the alpha and beta isoforms of myosin heavy chain? Because the ratio of alpha to beta in the sarcomere defines the relative contractility of the myocyte, and because this ratio depends upon species and developmental stage, I think it warrants a description. This is particularly relevant given the up-regulation of myosin heavy chain beta (fetal isoform) during the response to pressure overload on the heart (e.g. due to exercise or hypertension). Thoughts? EganioTalk 05:22, 23 November 2007 (UTC)

Revisions[edit]

I removed these lines: "Since the power stroke always moves the lever arm by the same angle, the length of the lever arm determines how fast the cargo will move". This is completely wrong, the velocity is determined by its ATPase rate. "Myosin V, for example, has a much longer neck region than myosin II, and therefore moves 30-40 nanometers with each stroke as opposed to only 5-10." This is also a terrible comparison, Myosin V is a 2 headed processive motor whereas Myosin II is non-processive. Therefore, Myosin V has a diffusional search component to its step size which can add 13 nm to its step size. —Preceding unsigned comment added by 76.124.95.228 (talk) 21:29, 26 June 2010 (UTC)

I thought it was the release of Pi that actually causes the movement in Myosin, not ATP hydrolysis.The Way Things Move: Looking Under the Hood of Molecular Motor Proteins, Ronald D. Vale and Ronald A. Milligan, Science April 2000 128.135.78.129 (talk) 15:33, 26 November 2008 (UTC)

-There are actually 2 components to the movement of myosin. The release of Pi from the myosin results in the powerstroke while attached to the actin. This was proven by Goldman in 87 or 88 (It's in Science) and for myosin V accounts for about 20-some nm of movement and is referred to as the working stroke. The gating is the 2nd part of the movement, and is believed to be from the release of ADP from the myosin-actin complex (the gated-gait nature paper by Viegel). The recovery stroke is the ATP hydrolysis while unbound to the actin (well it can actually happen while bound but it's negligible). -Myosin guy

I made some revisions to this page to attempt to clarify some nomenclature issues and I thought it made the most sense to combine the nomenclature with the evolution and family tree (since this is how we define the classes). Any comments? Medical geneticist (talk) 22:36, 8 July 2008 (UTC)

Added more referencesMedical geneticist (talk) 22:43, 9 July 2008 (UTC)

-If you are thinking about tackling this from a species perspective, don't even bother. There is really only a nomenclature consensus within mammalian myosins.

From the intro: "The term “myosin” was originally used to describe a group of similar, but nonidentical, ATPases found in striated and smooth muscle cells." From Pollard and Korn, 1973." I don't understand this quote. -Originally used -as in not anymore? And those ATPases he talks about, is that supposed to be the myosin (as described on the page) or some other molecule? The quote is so ambiguous I'm very tempted to remove it. The other option would be explaining it clearly, but I think that would be a rather backwards way to approach the topic. Akita86 (talk) 00:03, 24 January 2009 (UTC)

This is meant to give historical background to the concept that myosins, although originally thought to be restricted to muscle cells (hence, "myo"), are now known to exist in essentially all eukaryotic cells. There is no single "myosin" but rather a huge number of family members that share a basic similarity of binding to actin, hydrolyzing ATP (ATPases), and transducing that energy into force. Some have specialized functions in certain cell types, others are ubiquitous. --- Medical geneticist (talk) 18:33, 24 January 2009 (UTC)
Thank you. Historical context is important. I think it would be useful to contrast this quote with the current definition, possibly along the lines of what you just wrote. As it stands now, the quote seems out of context. Another user is also expressing confusion about this quote below. Akita86 (talk) 18:45, 24 January 2009 (UTC)
Point taken. I've made a small addition to the first paragraph to address this problem. Better? --- Medical geneticist (talk) 20:36, 25 January 2009 (UTC)

Time for a major overhaul?[edit]

I'd like to make this a pet project, to spruce up the myosin page and make it really good. If anyone else is interested, I'd be happy to discuss ways to reorganize and improve.Medical geneticist (talk) 22:43, 9 July 2008 (UTC)

Cardiac Muscle article link[edit]

"The term “myosin” was originally used to describe a group of similar, but nonidentical, ATPases found in striated and smooth muscle cells." Well that's a problem then. Because the "Cardiac Muscle" article is linking to this article on this myosin. 76.111.80.228 (talk) 20:33, 19 July 2008 (UTC)

I think that's ok because we use the term "myosin" to refer to a large number of structurally distinct myosins found across the eukaryotic phyla, many of which are highly divergent. What makes them part of the same gene family is their ability to bind actin, hydrolyze ATP, and transduce force. In multicellular organisms, many of the myosins have expression patterns restricted to certain types of cells (hence, striated muscle cells express a particular repertoire of myosins, smooth muscle cells express smooth muscle isoforms, and cardiac muscle expresses cardiac isoforms). When I have some more free time I'm hoping to expand this entry to clarify a bit. Medical geneticist (talk) 13:10, 22 July 2008 (UTC)
Oh. Oh, I get it. I was interpreting it to mean non-cardiac myosins instead of cardiac myosins, rather than myosins in general, including the cardiac ones. 76.111.80.228 (talk) 23:56, 3 September 2008 (UTC)

Myosin II polymerisation[edit]

Myosin II polymerises, to form the so-called 'thick filaments', or sometimes 'minifilaments', in non-muscle cells i think. The tail domain mediates the polymerisation.

Now, the thing about the polymerisation is that it works two ways. Firstly, monomers stick together pointing the same way, so that they can all interact with a parallel F-actin bundle and walk along it. But there's also an antiparallel interaction, which makes minifilaments bipolar, with a plus-end-seeking cluster of heads at each end - that's what enables them to generate tension when bound two actin bundles pointing in opposite directions, as in a muscle or stress fibre. Right?

How does that happen? The parallel polymerisation is easy enough to understand. Is the antiparallel association mediated by binding sites in the myosin, or by some separate crosslinker? ISTR that you can reconstitute contraction with just actin, myosin and ATP, which implies there's no crosslinker.

This page] says "bipolar complexes of myosin II form by interaction of antiparallel coiled coil tail domains". —Preceding unsigned comment added by 144.82.240.74 (talk) 17:51, 17 November 2008 (UTC)

EDIT: okay, a bit of pubmedication turns up the following papers:

[1] [2] [3]

All from Tom Pollard's lab, which look at assembly in some detail in amoeba (which i'm hoping is similar to the situation in vertebrate nonmuscle cells). First, you form antiparallel dimers, then those polymerise to tetramers and octamers. But not higher assemblies. This review talks a bit about assembly in muscle, and has some potentially useful references:

[4] —Preceding unsigned comment added by 144.82.240.74 (talk) 18:19, 17 November 2008 (UTC)

-There is also a huge dependence on the salt conditions for polymerization, which has been rather troublesome to replicate in vitro due to the physiological concentrations killing the myosin's motility.

Aminoacid sequence[edit]

What is the aminoacid sequence(s) of this protein?--79.116.66.97 (talk) 12:06, 19 May 2010 (UTC)

That's going to depend entirely on which species and which family member you're talking about (there are around 40 different myosin genes in humans alone). In general, the NCBI gene database is a good place to look up sequence information. If you can be more specific, I'm sure we can help you find what you're interested in. --- Medical geneticist (talk) 10:36, 7 June 2010 (UTC)