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Re: Keratin Preservation (was Ostrom Symposium)



At 13:20 -0500 10/3/99, Ralph W. Miller III wrote:

>CLAWS, BEAKS, SCALES AND FEATHERS: THE EVOLUTIONARY IMPLICATIONS OF KERATIN
>PRESERVATION IN THE FOSSIL RECORD
>
>Mary Higby Schweitzer, Dept. of Biology, Museum of the Rockies, Montana State
>University, Bozeman, MT  59717
>
>Keratin is the structural protein responsible for making skin waterproof and
>durable, and it is the key component of hair, nails, claws, and other
>epidermal
>structures.  The durability and "hardness" of keratinous elements is a
>result of
>the molecular composition and structure of these proteins.
>
>The keratins are a phylogenetically significant family of proteins.  Alpha
>keratin
>arose from alteration and subsequent divergence in a protein which
>constitutes the
>cytoskeletal system of epidermal cells.  This alteration arose with the
>vertebrates, and the cornified skin layers of all vertebrates contain alpha
>keratin.  Beta keratin, on the other hand, is a family of proteins which arose
>from an unidentified cellular precursor, sometime after the divergence of
>mammals,
>and so is unique to reptiles and birds among extant taxa.

[snip]

OK, I'm confused.  Keratin is keratin - it has one molecular formula (more
or less - there are about 30 known varieties).  There's two structural
forms of it - a helix (called alpha-keratin) and a pleated sheet (called
beta keratin).

Now, if this is what she's talking about, then, yes, all vertebrates have
alpha-helix keratin (I haven't been able to confirm in the short time I
looked that inverts don't). However, beta keratin did NOT arise after
mammals split off, since inverts produce it.  Silk and spiderweb, in fact,
are made of beta keratin.


Laurie Nyveen                                  lawrence@dsuper.net
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