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a variety of antigens containing acetylated
lysine. Obviously antibodies directed against
pan-acetyllysine proteins will vary widely in
their af
regulated by histone acetyltransferases and
histone deacetylase enzymes. Identi
cation of
the proteins involved is achieved through anti-
acetyllysine antibody selection as noted earlier.
This was achieved with mitosis, for example,
by synchronization of HeLa cells and then
immune-selecting proteins bearing acetyllysine
during mitosis with subsequent LC-MS/MS
identi
nity for any one protein. That means
that during enrichment of acetyllysine-bearing
proteins the ratio of proteins selected might
differ quantitatively from the distribution of
acetyllysine-carrying proteins in the mixture,
especially when approaching the
loading
cation. Fifty-one unique nonhistone
proteins were identi
capacity of the immunosorbent.
A very important aspect of antibody selec-
tion of acetyllysine-bearing proteins is recog-
nition
ed, including proteins
involved in RNA translation, RNA processing,
cell cycle regulation, transcription, chaperone
function, DNA damage repair, metabolism,
immune response, and cell structure.
94
Histone
deacetylase again played a role in regulating
the acetylation status of some of these proteins
but not others, suggesting a differential regula-
tory mechanism.
cation of
lysine acetylation sites can vary substantially
between antibodies. The majority of acetyl-
ated lysine residues identi
that
site-speci
cid i
ed using a mono-
clonal antibody cocktail, for example, were
distinct from those enriched by polyclonal
antibodies.
Lysine acetylation is widely associated with
histones but is found in many nonhistone
proteins as well, such as p53 and other proteins
in cancer.
Methylation
Methylation of arginine and lysine occurs in
multiple ways (
Figure 7
), all of which are
Interestingly,
their acetylation is
CH
3
methylation of arginine
methylation of lysine
N-CH
3
C=NH
CH
3
CH
3
CH
3
NH
N
+
NH
2
NH
N
CH
3
CH
3
CH
3
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
NH
2
SAM
PLMT
SAM
PLMT
SAM
PLMT
NH-CH
3
CH
2
CH
2
CH
2
CH
2
CH
2
C=NH
C=NH
-N-CH-C-
O
CH
2
CH
2
CH
2
CH
2
NH
NH
H
-N-CH-C-
O
-N-CH-C-
O
-N-CH-C-
O
-N-CH-C-
O
CH
2
SAM
PAMT(1/2)
CH
2
H
H
H
H
CH
2
CH
2
NH-CH
3
CH
2
CH
2
C=N-CH
3
-N-CH-C-
O
-N-CH-C-
O
NH
H
H
CH
2
CH
2
CH
2
-N-CH-C-
O
H
FIGURE 7
Illustrations of arginine and lysine methylation in proteins. S-adenosyl-L-methionine
¼
SAM. Protein arginine
methyltransferase type 1
¼
PAMT(1). Protein arginine methyltransferase type 2
¼
PAMT(2). Protein lysine methyltransferase
¼
PLMT.
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