The acylation of megakaryocyte proteins: glycoprotein IX is primarily
myristoylated while glycoprotein Ib is palmitoylated
PK Schick and J Walker
Cardeza Foundation for Hematologic Research, Jefferson Medical College,
Thomas Jefferson University, Philadelphia, PA 19107-5099, USA.
The acylation of megakaryocyte proteins was studied with special emphasis
on the myristoylation and palmitoylation of the glycoprotein (GP) Ib
complex. Guinea pig megakaryocytes were purified and separated into
subpopulations at different phases of maturation. Cells were incubated with
[3H]myristate, [3H]palmitate, or [3H]acetate to study endogenous protein
acylation. Cycloheximide was used to distinguish between cotranslational
and posttranslational acylation and hydroxylamine to distinguish between
thioester and amide linkages. After incubations, delipidated proteins or
GPIb complex subunits, immunoprecipitated with PG-1, AN-51 or FMC-25
monoclonal antibody, were separated by sodium dodecyl
sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and assessed by
fluorography. Radiolabeled fatty acids bound to GPIX and GPIb were also
analyzed by high pressure liquid chromatography (HPLC) and scintillation
spectrometry. With [3H]myristic acid and [3H]acetate, GPIX was found to be
a major myristoylated protein in megakaryocytes and CHRF-288 cells.
Myristic acid was linked to GPIX by an amide bond, and this process
occurred cotranslationally. With [3H]acetate, GPIb was primarily
palmitoylated, but with [3H]myristate, GPIb was acylated with about equal
mounts of myristic acid and palmitic acids. Both fatty acids were linked to
GPIb by thioester bonds, and acylation was posttranslational. The
myristoylation of GPIX while the palmitoylation of GPIb occurred throughout
megakaryocyte maturation. Myristoylation and palmitoylation may have
different functions relevant to the assembly of the GPIb complex in
megakaryocytes.
Volume 87,
Issue 4,
pp. 1377-1384,
02/15/1996
Copyright © 1996 by The American Society of Hematology
