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Sllde
Ms lnvolvlng addlLlon lnclude
acylaLlon
of Lhe proLeln Lermlnus n group usually aL Lhe aceLyl Lhe addlLlon of an aceLylaLlon
group eg meLhyl eLhyl alkyl f an Lhe addlLlon o alkylaLlon
resldues hls ls a arglnlne or lyslne group usually aL meLhyl Lhe addlLlon of a meLhylaLlon
Lype of alkylaLlon
demeLhylaLlon
Lermlnus aL C amldaLlon
resldues wlLh a bloLln appendage lyslne acylaLlon of conserved bloLlnylaLlon
formylaLlon
vlLamln k dependenL on ylaLlon carbox gamma
resldues Lo Lubulln and some oLher acld gluLamlc enL llnkage of coval gluLamylaLlon
Lamylase polyglu Lubulln See
proLelns
or serlne hydroxylyslne asparaglne group Lo elLher glycosyl Lhe addlLlon of a glycosylaLlon
whlch ls regarded as a glycaLlon ulsLlncL from glycoproLeln resulLlng ln a Lhreonlne
nonenzymaLlc aLLachmenL of sugars
C Lubulln resldues Lo Lhe glyclne covalenL llnkage of one Lo more Lhan glycylaLlon
Lermlnal Lall
moleLy may be covalenLly aLLached heme
hydroxylaLlon
Lhyrold hormones eg of lodlnaLlon
group eg farnesol and geranylgeranlol lsoprenold Lhe addlLlon of an lsoprenylaLlon
aLLachmenL of a llpoaLe funcLlonallLy llpoylaLlon
prenylaLlon
formaLlon Cl anchor
myrlsLoylaLlon
farnesylaLlon
geranylgeranylaLlon
or derlvaLlves Lhereof may be covalenLly aLLached nucleoLldes
osylaLlon rlb Au
aLLachmenL flavln
oxldaLlon
pegylaLlon
may be covalenLly aLLached phosphaLldyllnoslLol
coenzyme phosphopanLeLhelnyl moleLy from Lhe addlLlon of a phosphopanLeLhelnylaLlon
rlbosomal pepLlde and leuclne blosynLhesls as ln faLLy acld polykeLlde non A
or Lhreonlne Lyroslne serlne group usually Lo phosphaLe Lhe addlLlon of a phosphorylaLlon
hlsLldlne
formaLlon pyrogluLamaLe
lsomerase prolyl by prollne of racemlzaLlon
arglnylaLlon medlaLlon addlLlon of amlno aclds such as LnA
Lyroslne Lhe addlLlon of a sulfaLe group Lo a sulfaLlon
selenoproLelns ln selenlum LranslaLlonal lncorporaLlon of co SelenoylaLlon
SulfaLlon
Ms nvovng addton of other protens or peptdes
SLlmulaLed Cene llnkage Lo Lhe lSC proLeln lnLerferon covalenL lSCylaLlon Lhe
relaLed MCdlfler Small ublqulLln SuMC proLeln llnkage Lo Lhe covalenL Lhe SuMCylaLlon
llnkage Lo Lhe proLeln ublqulLln covalenL Lhe ublqulLlnaLlon
Ms nvovng changng the chemca nature of amno acds
clLrulllne Lo arglnlne Lhe converslon of demnaton or clLrulllnaLlon
asparLlc acld Lo asparaglne or acld gluLamlc Lo gluLamlne Lhe converslon of deamldaLlon
Ms nvovng structura changes
amlno aclds cysLelne Lhe covalenL llnkage of Lwo dlsulflde brldges
cleavage of a proLeln aL a pepLlde bond cleavage proLeolyLlc
ase exampes
lnsulln cleavage and formaLlon of dlsulflde brldges durlng Lhe producLlon of
nA polymerase conLrol by chromaLln as regulaLlon of LranscrlpLlon hlsLones M of
sLrucLure
nA polymerase ll M of nA polymerase ll as regulaLlon of LranscrlpLlon
xterna Lnks
ulfferenLlal M ueLecLlon afLer mass specLromeLry delLaMasses
ranslaLlonal A CompuLaLlonal roLocol for ldenLlflcaLlon of osL Server AuLoMoLlf
ModlflcaLlons ln roLeln Sequences
of a LargeL proLeln ln cells phosphorylaLlon speclflc luncLlonal analyses for slLe
Sllde
renyaton
renylaLlon refers Lo Lhe addlLlon of Lhe carbon farnesyl group or Lhe carbon
geranylgeranyl group Lo accepLor proLelns boLh of whlch are lsoprenold compounds
derlved
he lsoprenold groups are aLLached Lo cysLelne synLheLlc paLhway cholesLerol blo from
Lhe
resldues aL Lhe carboxy Lermlnus of proLelns ln a LhloeLher llnkage CSC A common
consensus sequence aL Lhe CLermlnus of prenylaLed proLelns has been ldenLlfled and ls
composed of CAAx where C ls cysLelne A ls any allphaLlc amlno acld excepL alanlne and x
ls Lhe CLermlnal amlno acld ln order for Lhe prenylaLlon reacLlon Lo occur Lhe Lhree C
Lermlnal amlno aclds AAx are flrsL removed lollowlng aLLachmenL of Lhe prenyl group Lhe
carboxylaLe of Lhe cysLelne ls meLhylaLed ln a reacLlon uLlllzlng SadenosylmeLhlonlne as
Lhe
meLhyl donor
ln addlLlon Lo numerous prenylaLed proLelns LhaL conLaln Lhe CAAx consensus
prenylaLlon ls
known Lo occur on proLelns of Lhe A famlly of ASrelaLed CproLelns here are aL leasL
proLelns ln Lhls famlly LhaL are prenylaLed aL elLher a CC or CxC elemenL ln Lhelr C
Lermlnl he A famlly of proLelns are lnvolved ln slgnallng paLhways LhaL conLrol
lnLracellular membrane Lrafflcklng
Some of Lhe mosL lmporLanL proLelns whose funcLlons depend upon prenylaLlon are
Lhose
LhaL modulaLe lmmune responses hese lnclude proLelns lnvolved ln leukocyLe moLlllLy
acLlvaLlon and prollferaLlon and endoLhellal cell lmmune funcLlons lL ls Lhese lmmune
modulaLory roles of many prenylaLed proLelns LhaL are Lhe basls for a porLlon of Lhe anLl
lnhlblLlng drugs due Lo a of cholesLerol synLhesls class sLaLln lnflammaLory acLlons of
Lhe
reducLlon ln Lhe synLhesls of farnesylpyrophosphaLe and geranylpyrophosphaLe and Lhus
reduced exLenL of lnflammaLory evenLs CLher lmporLanL examples of prenylaLed proLelns
lnclude Lhe oncogenlc Cblndlng and hydrolyzlng proLeln AS and Lhe subunlL of Lhe
vlsual proLeln Lransducln boLh of whlch are farnesylaLed ln addlLlon numerous Cblndlng
cascades have slgnal LransducLlon proLelns of and hydrolyzlng proLelns Lermed C
subunlLs modlfled by geranylgeranylaLlon
ependent Modfcatons Vtamn back Lo Lhe Lop
as a cofacLor lnclude prollne and vlLamln C LhaL depend upon ModlflcaLlons of proLelns
lyslne hydroxylaLlons and carboxy Lermlnal amldaLlon he hydroxylaLlng enzymes are
ldenLlfled as prolyl hydroxylase and lysyl hydroxylase he donor of Lhe amlde for CLermlnal
amldaLlon ls glyclne he mosL lmporLanL hydroxylaLed proLelns are Lhe collagens Several
pepLlde hormones such as oxyLocln and vasopressln have CLermlnal amldaLlon
ependent Modfcatons Vtamn k back Lo Lhe Lop
ls a cofacLor ln Lhe carboxylaLlon of gluLamlc acld resldues he resulL of Lhls Lype vlLamln
k
of reacLlon ls Lhe formaLlon of a carboxygluLamaLe gammacarboxygluLamaLe referred Lo
as a gla resldue
tructure of a f resdue
cascade ls crlLlcal blood cloLLlng he formaLlon of gla resldues wlLhln several proLelns of
Lhe
for Lhelr normal funcLlon he presence of gla resldues allows Lhe proLeln Lo chelaLe calclum
lons and Lhereby render an alLered conformaLlon and blologlcal acLlvlLy Lo Lhe proLeln he
coumarlnbased anLlcoagulanLs warfarln and dlcumarol funcLlon by lnhlblLlng Lhe
carboxylaLlon reacLlon
Sllde
Mechanlsm of synLhesls of membrane bound or secreLed proLelns lbosomes engage Lhe L
membrane Lhrough lnLeracLlon of Lhe slgnal recognlLlon parLlcle S ln Lhe rlbosome wlLh
Lhe S recepLor ln Lhe L membrane As Lhe proLeln ls synLheslzed Lhe slgnal sequence ls
passed Lhrough Lhe L membrane lnLo Lhe lumen of Lhe L AfLer sufflclenL synLhesls Lhe
slgnal pepLlde ls removed by Lhe acLlon of slgnal pepLldase SynLhesls wlll conLlnue and lf
Lhe
proLeln ls secreLed lL wlll end up compleLely ln Lhe lumen of Lhe L lf Lhe proLeln ls
membrane assoclaLed a sLop Lransfer moLlf ln Lhe proLeln wlll sLop Lhe Lransfer of Lhe
proLeln Lhrough Lhe L membrane hls wlll become Lhe membrane spannlng domaln of Lhe
proLeln
Sllde
However, recent evidence has shown that lysine methylation, similar to other covalent
modiIications, can be transient and dynamically regulated by an opposing demethylation
activity. Recent Iindings indicate that methylation oI lysine residues aIIects gene expression
not only at the level oI chromatin, but also by modiIying transcription Iactors.
Additional nitrogen methylations are Iound on the imidazole ring oI histidine, the guanidino
moiety oI arginine and the Rgroup amides oI glutamate and aspartate. Methylation oI the
oxygen oI the Rgroup carboxylates oI gutamate and aspartate also takes place and Iorms
methyl esters. Proteins can also be methylated on the thiol Rgroup oI cysteine.
As indicated below, many proteins are modiIied at their Cterminus by prenylation near a
cysteine residue in the consensus CAAX. Following the prenylation reaction the protein is
cleaved at the peptide bond oI the cysteine and the carboxylate residue is methylated by a
prenylated protein methyltransIerase. One such protein that undergoes this type oI
modiIication is the protooncogene RAS.
Slide
In lymphoid organs endothelial cells express oligs recognised by Lselectin on lymphocytes,
causing them to loiter
At inIlammation sites endothelial cells express selectins to catch white blood cells and
platelets
Collaboration with integrins
Slide
Some proteoglycans secreted as mucus, etc
Slide
Apical outside e.g. Iacing gut
Tryp. uses phospholipases in plasma membrane
Slide
Most proteins undergo proteolytic cleavage Iollowing translation. The simplest Iorm oI this is
the removal oI the initiation methionine. Many proteins are synthesized as inactive
precursors
that are activated under proper physiological conditions by limited proteolysis. Pancreatic
enzymes and enzymes involved in clotting are examples oI the latter. Inactive precursor
proteins that are activated by removal oI polypeptides are termed proproteins.
A complex example oI posttranslational processing oI a preproprotein is the cleavage oI
Peptide Hormones opiomelanocortin POMC synthesized in the pituitary see the prepro
page Ior discussion oI POMC. This preproprotein undergoes complex cleavages, the
pathway
oI which diIIers depending upon the cellular location oI POMC synthesis.
. Since insulin is secreted Irom the pancreas it insulin Another is example oI a preproprotein
is
has a prepeptide. Following cleavage oI the amino acid signal peptide the protein Iolds
into proinsulin. Proinsulin is Iurther cleaved yielding active insulin which is composed oI two
peptide chains linked togehter through disulIide bonds.
Still other proteins oI the enzyme class are synthesized as inactive precursors called
zymogens. Zymogens are activated by proteolytic cleavage such as is the situation Ior
several
cascade. blood clotting proteins oI the
Slide
Phosphorylation
Posttranslational phosphorylation is one oI the most common protein modiIications that
occurs in animal cells. The vast majority oI phosphorylations occur as a mechanism to
regulate the biological activity oI a protein and as such are transient. In other words a
phosphate or more than one in many cases is added and later removed.
Physiologically relevant examples are the phosphorylations that occur in glycogen synthase
and glycogen phosphorylase in hepatocytes in response to glucagon release Irom the
pancreas. Phosphorylation oI synthase inhibits its activity, whereas, the activity oI
phosphorylase is increased. These two events lead to increased hepatic glucose delivery to
the
blood.
The enzymes that phosphorylate proteins are termed kinases and those that remove
phosphates are termed phosphatases. Protein kinases catalyze reactions oI the Iollowing
type
ATP protein phosphoprotein ADP
In animal cells serine, threonine and tyrosine are the amino acids subject to phosphorylation.
The largest group oI kinases are those that phsophorylate either serines or threonines and
as
such are termed serine/threonine kinases. The ratio oI phosphorylation oI the three diIIerent
amino acids is approximately // Ior serine/threonine/tyrosine.
Although the level oI tyrosine phosphorylation is minor, the importance oI phosphorylation oI
this amino acid is proIound. As an example, the activity oI numerous growth Iactor receptors
is controlled by tyrosine phosphorylation.
Slide
gure Fi binds very tightly to GDP, a guanine nucleotide exchange Iactor see Because eIF
B, is required to cause GDP release so that a new GTP molecule can , designated eIF
is inhibited when it is . The reuse oI eIF A Figure can be reused bind and eIF
phosphorylated the phosphorylated eIF binds to eIFB unusually tightly, inactivating eIF
B. There is more eIF than eIFB in cells, and even a Iraction oI phosphorylated eIF can
trap nearly all oI the eIFB. This prevents the reuse oI the nonphosphorylated eIF and
. B Figure greatly slows protein synthesis
Regulation oI the level oI active eIF is especially important in mammalian cells, being part
oI the mechanism that allows them to enter a nonproliIerating, resting state called G
in
which the rate oI total protein synthesis is reduced to about oneIiIth the rate in proliIerating
cells
Slide
The molecular switches Iall into two main classes that operate in diIIerent ways, although in
both cases it is the gain or loss oI phosphate groups that determines whether the protein is
active or inactive. The largest class consists oI proteins that are activated or inactivated by
. For these proteins, the switch is thrown in one Chapter phosphorylation discussed in
direction by a protein kinase, which adds one or more phosphate groups to the signaling
protein, and in the other direction by a protein phosphatase, which removes the phosphate
proteins in a third oI the . It is estimated that one A Figure groups Irom the protein
eucaryotic cell are phosphorylated at any given time.
The other main class oI molecular switches involved in signaling are Pbinding proteins
. These switch between an active state when GTP is bound and an er Chapt discussed in
inactive state when GDP is bound. Once activated, they have intrinsic GTPase activity and
. There are two B Figure shut themselves oII by hydrolyzing their bound GTP to GDP
major types oI GTPbinding proteins large trimeric GTPbinding proteins also called G
, and B Figure ors see linked recept protein which relay the signals Irom G proteins,
small monomeric GTPases also called monomeric GTPbinding proteins. The latter also
help to relay intracellular signals, but in addition they are involved in regulating vesicular
traIIic and many other processes in eucaryotic cells.
Slide
The mechanism is similar to the one just discussed that drives allosteric protein shape
changes
by GTP hydrolysis. Because a great deal oI Iree energy is released when ATP or GTP is
hydrolyzed, it is very unlikely that the nucleotidebinding protein will undergo the reverse
shape change needed Ior moving backward since this would require that it also reverse the
ATP hydrolysis by adding a phosphate molecule to ADP to Iorm ATP
Slide
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