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Journal of Bacteriology, June 2000, p. 3452-3459, Vol. 182, No. 12
Department of Biochemistry, Virginia
Polytechnic Institute and State University, Blacksburg, Virginia
24061
Received 10 December 1999/Accepted 23 March 2000
The extreme acidothermophilic archaeon Sulfolobus
solfataricus harbors a membrane-associated protein kinase
activity. Its solubilization and stabilization required detergents,
suggesting that this activity resides within an integral membrane
protein. The archaeal protein kinase utilized purine nucleotides as
phosphoryl donors in vitro. A noticeable preference for nucleotide
triphosphates over nucleotide diphosphates and for adenyl nucleotides
over the corresponding guanyl ones was observed. The molecular mass of the solubilized, partially purified enzyme was estimated to be
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
The Archaeon Sulfolobus solfataricus
Contains a Membrane-Associated Protein Kinase Activity That
Preferentially Phosphorylates Threonine Residues In Vitro
and
125
kDa by gel filtration chromatography. Catalytic activity resided in a
polypeptide with an apparent molecular mass of
67 kDa by sodium
dodecyl sulfate-polyacrylamide gel electrophoresis. Challenges with
several exogenous substrates revealed the protein kinase to be
relatively selective. Only casein, histone H4, reduced carboxyamidomethylated and maleylated lysozyme, and a peptide modeled
after myosin light chains (KKRAARATSNVFA) were
phosphorylated to appreciable levels in vitro. All of the
aforementioned substrates were phosphorylated on threonine residues,
while histone H4 was phosphorylated on serine as well. Substitution of
serine for the phosphoacceptor threonine in the myosin light chain
peptide produced a noticeably inferior substrate. The protein kinase
underwent autophosphorylation on threonine and was relatively
insensitive to a set of known inhibitors of "eukaryotic" protein kinases.
*
Corresponding author. Mailing address: Department of
Biochemistry (0308), Virginia Polytechnic Institute and State
University, Blacksburg, VA 24061. Phone: (540) 231-4317. Fax: (540)
231-9070. E-mail: pjkennel{at}vt.edu.
Present address: USDA Agricultural Research Service, College
Station, TX 77845.
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