Nic Tamzek

Ah. A recent Discover magazine article alludes to the 9+2 (=11) protofibrils-make-a-microfibril-cable idea:

<a href="http://www.discover.com/feb_02/featbiology.html" target="_blank">http://www.discover.com/feb_02/featbiology.html</a>

...so it sounds like the "3 helices make a protofibril" is wrong and outdated, but the "9+2 protofibrils make a microfibril cable in hair" idea might still be right. Can you confirm or deny, Randy?

nic

Randy

The 2-4-8-32 aggregation pattern seems to be common to all keratin microfibrils, whether in hair, skin or nail and the two chain coiled coil is common to all intermediate filament proteins.
You can find some info from the 3rd edition Biochemistry by Van Holde and Mathews at
<a href="http://www.awlonline.com/mathews/ch06/fi6p11.htm" target="_blank">http://www.awlonline.com/mathews/ch06/fi6p11.htm</a>
I have the first edition of this book printed in 1989 and it still has the incorrect 3 chain model. I think it was corrected in the second edition.

Here are a few references. Peter Steinert at NIH is probably the world’s foremost expert on keratin structure and a lot of the references are to his work.

Parry, D.A.D. and North, A.C.T. (1998) Hard a-keratin keratin intermedite filament chains:Substructure of the N- and C- terminal domains and the predicted structure and function of the c-teminal domains of type I and type II chains. J.Structural Biology 122, 67.

Parry, D.A.D., Steven, A.C. and Steinert, P.M. (1985) The coiled-coil molecules of intermediate filaments consist of two parallel chains in exact axial register. Biochem Biophys Res Commun 127, 1012.

Steinert, P.M. (1991) Organization of coiled-coil molecules in native keratin 1/keratin 10 intermediate filaments:Evidence for alternating rows of antiparallel in-register and anti-parallel staggered molecules. J.Structural Biology 107, 157.

Steinert, P.M. (1993) Structure, Function and Dynamics of Keratin Intermediate Filamaments. J Invest Dermatol 100, 729.

Steinert, P.M. and Freedberg, I.M. (1991) Molecular and cellular biology of keratins. In: L.A. Goldsmith (Ed.), Physology, Biochemistry, and Molecular Biology of the Skin. Vol.2, Oxford University Press, New York, p. 113.

Steinert, P.M., Marekov, L.N., Fraser, R.D.B. and Parry, D.A.D. (1993) Keratin intermediate filament structure: Crosslinking studies yield quantitative information on molecular dimensions and mechanics of assembly. J Mol Bio 230, 436.

Steinert, P.M. and Parry, D.A. (1993) The conserved H1 domain of the type II keratin 1 chain plays an essential role in the alignment of nearest neighbor molecules in mouse and human keratin 1/keratin 10 intermediate filaments at the two- to four-molecule level of structure. J Biol Chem 268, 2878.

Wilk, K.E., James, V.J. and Amemiya, Y. (1995) The intermediate filament structure of human hair. Biochim Biophys Acta 1245, 392.

Randy

Randy

Sarfati is clearly a master of out of context quoting in the true tradition of Gish.

If my information on feather keratins has been a blessing to you please send me a donation.

Randy

Nic Tamzek

Thanks Randy, it sounds like the 9+2 arrangement of protofibrils into a microfibril is outdated also. Wonder where it got started though, I found several (non-authoritative) hair websites still saying it. Perhaps everybody went through the same textbook as me...

9+2 just seemed like a very peculiar similarity to be shared between hair and a cilium, that's why I brought it up...

Thanks for the refs, I'll look up some Steinert and if I turn anything of interest up I'll report back.

nic

Randy

I think it came from Fraser and McRea's X-ray work on wool in the 60's or maybe 70's. I know I learned it at one time. It was in all texts that covered the subject including Van Holde and Mathews which the chem department here uses as a biochem text. Hair and wool proteins are very difficult to work with because it is so hard to get them out. You need to use 8 molar urea and a reducing agent such as DTT so by the time you isolate them their structure is pretty well messed up. At lot of the original work on keratin fibers was done with wool because of the economic importance of understanding the behavior of wool fibers in textiles. I'll look into it somemore tomorrow if I get time.

BTW the Wilk BBA paper probably gives the most detail on the microfibril structurein cross section. Steinert's work shows that the coiled coils are parallel and in register and the 4-chain structures form from two anti-parallel coiled coils that are not necessarily in register. You will find that there are some highly conserved and highly varible regions in keratins and the conserved regions probably play a role in aggregation to the microfibril.

Randy

GeoTheo

This is not a very scientific comment, but I was just at a State fair recently and there were some chickens that seemed to have feathers where the scales on their legs are supposed to be.
This leads me to believe that a genetic mutation caused the sequence for the leg scales to be read a little differently and so they came out feathers. This would lead me to believe that the feathers and the scales are similar genetically.
It was just a thought that occured to me. I was with a bunch of YEC's so I kept my obsevation to myself.

Blinn

I've pondered that possibility also.

Those chickens are really cool...



Some other birds that have feathered feet inclue ptarmigans and the snowy owl, obviously cold climate adaptations.

Boro Nut

My theory is that feathered dinosaurs were selectively bred by cavemen for writing purposes before the invention of the biro. If you would like to subscribe to this theory it is on special offer at only £5.99 per month.

Boro Nut

Also available in paperback.

Randy

There are a number of ways that bird scales can be converted into feathers. Reticulate scales can be made to produce feathers by treatment with retinoic acid.

Hardy, M.H., Dhouailly, D. and Sengel, P. (1981) Scales into feathers--an effect of retinoic acid on tissue interactions in the developing chick. Ann N Y Acad Sci 359, 394-395.

Fisher, C.J., Knapp, L.W. and Sawyer, R.H. (1988) Retinoic acid induction of featherlike structures from reticulate scales. Teratology 38, 321-328.

Mutations in beta catinen may cause the skin to express feathers rather than scales

Widelitz, R.B., Jiang, T.X., Lu, J. and Chuong, C.M. (2000) beta-catenin in epithelial morphogenesis: conversion of part of avian foot scales into feather buds with a mutated beta-catenin. Dev Biol 219, 98-114.

And changes in BMP expression may also cause feather to form where scales would normally form.

Zou, H. and Niswander, L. (1996) Requirement for BMP signaling in interdigital apoptosis and scale formation. Science 272, 738-741.

Apparently the epithelial cells that produce scales are at least bi-potent and can make feathers or at least feather-like structures under the right stimulus.

Randy

GeoTheo

Cool! (about the acid information)
And thanks for the photo. That was just what their legs looked like. Some even had feathers covering their entire head and some had heads like vultures with no feathers.