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better beta keratin
Laurie Nyveen wrote:
> >The keratins are a phylogenetically significant family of proteins.
> >arose from alteration and subsequent divergence in a protein which
> >constitutes the
> >cytoskeletal system of epidermal cells. This alteration arose with
> >vertebrates, and the cornified skin layers of all vertebrates
> >keratin. Beta keratin, on the other hand, is a family of proteins
> >from an unidentified cellular precursor, sometime after the
> >and so is unique to reptiles and birds among extant taxa.
> OK, I'm confused. Keratin is keratin - it has one molecular formula
> or less - there are about 30 known varieties). There's two structural
> forms of it - a helix (called alpha-keratin) and a pleated sheet
> beta keratin).
> Now, if this is what she's talking about, then, yes, all vertebrates
> alpha-helix keratin (I haven't been able to confirm in the short
> looked that inverts don't). However, beta keratin did NOT arise after
> mammals split off, since inverts produce it. Silk and spiderweb, in
> are made of beta keratin.
I'm not surprised you're confused. Yes, keratin is keratin. Alpha
keratin definitely has an alpha-helix secondary structure. I don't
know about the beta keratin in feathers.
Unfortunately, a lot of molecular biologists use the term beta keratin
to refer to various fibrous proteins with a beta pleated sheet
structure. Like fibroin, the moth silk protein. As far as I know,
these 'beta keratins' aren't related to vertebrate keratins. I don't
know if they're even related to each other.
I hope this makes things less confusing.
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