protein function enzyme regulation biosignalling n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Protein Function/Enzyme Regulation/Biosignalling PowerPoint Presentation
Download Presentation
Protein Function/Enzyme Regulation/Biosignalling

Loading in 2 Seconds...

play fullscreen
1 / 58

Protein Function/Enzyme Regulation/Biosignalling - PowerPoint PPT Presentation


  • 132 Views
  • Uploaded on

Protein Function/Enzyme Regulation/Biosignalling. Chpts. 5, 6, 12. 1 o , 2 o , 3 o , 4 o Structures REMEMBER??. Structure defines function If >1 polypeptide chain, 4 o structure Chains not independent Book: Proteins are dynamic structures. Definitions (Chpt. 5).

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Protein Function/Enzyme Regulation/Biosignalling' - trish


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
1 o 2 o 3 o 4 o structures remember
1o, 2o, 3o, 4o Structures REMEMBER??
  • Structure defines function
  • If >1 polypeptide chain, 4o structure
    • Chains not independent
  • Book: Proteins are dynamic structures
definitions chpt 5
Definitions (Chpt. 5)
  • Ligand – bound reversibly to prot
  • Binding site – where ligand binds
    • Complementarity
  • Induced fit – protein flexes  greater complementarity
  • (What do all of these characteristics remind you of?)
protein ligand binding
Protein/Ligand Binding
  • May be regulated by another molecule
    • May be second ligand w/ second binding site
  • Second ligand interaction  flexing  change in ability of first ligand to bind
    • First ligand may bind better or worse under influence of second ligand
hemoglobin hb
Hemoglobin (Hb)
  • 4 polypeptide chains + 4 heme grps
  • MW 64,5000

old book

protein globin
Protein (Globin)
  • Globular
  • 4 hydrophobic pockets
  • 4o structure due to interaction ~30 aa’s
  • a/b subunits interact (not a/a or b/b)
    • Mostly hydrophobic interactions, some ionic
slide8
Heme
    • Protophorphyrin ring
    • Binds single Fe as Fe+2
    • Sim to pigments
    • Resonance (electron transport, color, UV absorbance)
fe held in heme heme held in hb
Fe Held in Heme; Heme Held in Hb
  • 6 Coordination sites for heme Fe
    • 4 Bind N’s of protoporphyrin ring
    • 1 Binds globin His R grp N
    • 1 Binds O2
      •  Changes in heme electronic prop’s
      •  Color change
      • Fe can also bind CO
slide12
Globin may be in T state or R state
    • T state more stable w/out O2
    • O2 prefers to bind globin in R state (either poss.)
    • Bound O2 stabilizes R
o 2 binding to heme influences globin
O2 Binding to Heme Influences Globin
  • T state (stable deoxyHb) binds O2
  •  Shift in globin conform’n
    • a, b subunits slide, rotate
    • b subunits closer
  • R state results
  • O2 binding @ Fe  incr’d planarity of heme  altered interactions of R grps of nearby aa’s
imptc to hb function transport o 2
Imptc to Hb Function (Transport O2)
  • O2 must be reversibly bound to Hb, but tight enough for transport
  • Binding of 1 O2 molecule causes TR
    • R state now stabilized
    • Subunits have been effected
  • Now easier for 2nd O2 to bind
  • 3rd, 4th O2’s
    • R state strengthened w/ each O2 added
allosteric protein
Allosteric Protein
  • Ligand binding @ one site affects binding abilities @ other sites on same protein
  • Due to conform’l changes  altered binding site(s)
  • Hemoglobin example
    • O2 = activator (stimulator)
    • Positive cooperativity among subunits
slide20
Can be treated mathematically
    • Similar to Ka, Kd
    • P + nL  PLn
      • P = Protein
      • L = ligand
    • q= binding sites occ’d/total binding sites
  • Based on fraction of binding sites occupied, derive Hill coefficient (hH)
    • = 1, no cooperative binding
    • < 1, negative cooperativity
    • 1, positive cooperativity
models for cooperativity
Models for Cooperativity
  • Monod
    • “All or nothing”
    • No subunit in any independent conformation
    • Ligand binds any, but prefers one
slide23
Koshland (Sequential)
    • Subunits more independent
    • One subunit acts as modulator
      • Conform’l change influences conform’l changes in other subunits
    • “Graded effects”
sickle cell anemia
Sickle Cell Anemia
  • Mutation  single improper aa in Hb globin
    • b chain Glu  Val
    • Now – charge  uncharged side chain
    •  “sticky” hydrophobic pt @ outer Hb surface
  • DeoxyHb mol’s associate w/ each other
  •  Strand, fiber form’n
  •  Long, thin crescent rbc’s
allosteric effects regulate some enz activity in metabolism
Allosteric Effects Regulate Some Enz Activity in Metabolism
  • Metab pathways mediated by enzymes
    • Several rxns in succession
    • Each rxn catalyzed by partic enzyme
    • P rxn 1 becomes S for rxn 2, etc.
enzymes can be inhibited
Enzymes Can Be Inhibited
  • Product inhib’n
    • Enz may be inhib’d by its own P
    • Inverse relationship of [P] and further P synthesis
    • P acts as competitive inhibitor
      • Resembles S
      • Fits enz active site
      • Competes
      • Inhib’n overcome
slide30
Feedback inhibition
    • Enz may be inhib’d by metabolite from further down pathway
    • L-ileu prevents form’n
    • Inhibits thr dehydratase
      • No other
    • Thr dehydratase = regulatory enzyme
      • Regulates pathway
regulatory enzymes
Regulatory Enzymes
  • Catalyze slowest step
  • Stim’d or inhibited
  • Commonly 1st
  • Point of commitment
  • May be allosteric OR controlled by covalent modification
allosteric regulatory enzymes
Allosteric Regulatory Enzymes
  • REMEMBER how Hb worked
  • Modulated
  • >1 binding site
    • Binding of S to one site affects other binding site(s)
    • Both need not be catalytic
      • Often 1 regulatory
    • Both specific for S or modulator
    • Often on diff subunits
slide35
Modulator binding at regulatory site  conform’l change at catalytic site
    • May be harder or easier for S to bind
    • Conform’l changes due to noncovalent interactions
altered kinetics of allosteric enzymes
Altered Kinetics of Allosteric Enzymes
  • M-M model hyperbolic
  • Allosteric model sigmoidal
    • If modulator stimulates, more hyperbolic
    • If modulator inhibits, more sigmoidal
  • KM changes
covalently modified regulatory enzymes
Covalently Modified Regulatory Enzymes
  • Also controlled through modulators
  • Now modulator covalently bound
    • At some funct’l grp of aa of enz 1o structure
    • Need OTHER enz’s to catalyze binding of modulator
    • Need EVEN OTHER enz’s to catalyze lysis of modulator
    • So have groups of enzymes
  • Not necessarily subunits that interact
covalent modification at reg enz funct l grps
Covalent Modification at Reg Enz Funct’l Grps
  • Could disrupt entire 2o, 3o structure
  • Could inhibit S approach
  • Could inhibit S fit
  • Could modify funct’l grps impt to catalysis
types of modification
Types of Modification
  • Phosphorylation Nucleotidation
  • ADP-ribosylation Methylation/acetylation
glycogen phosphorylase example
Glycogen Phosphorylase Example
  • Glycolysis reg enz
  • 2 subunits, each w/ ser (what’s it’s funct’l grp?)
  • Cleaves glycogen (what’s it made of?)
    • Releases glu then phosphorylates glu
slide44
2 forms of enz (a = active, b = inactive)
  • 2 associated enz’s
    • Phosphorylase kinase cat’s b  a
      • Active form – phosphorylated
      • W/ transfer of Pi from ATP
    • Phosphorylase phosphatase cat’s a  b
      • W/ hydrolysis Pi
slide46
Phosph’n interferes w/ stabilizing ionic interactions
    • Changes folding (what type of structure (1o, etc.) is most impt to folding?)
    • New interactions between diff aa’s
    • Incr’s catalytic activity
  • a, b forms differ in 2o, 3o, 4o structures also
    • So some allosteric properties
another kinase may activate glycogen phosphorylase
Another Kinase May Activate Glycogen Phosphorylase
  • Protein kinase A is modulated also
  • Works through 2nd messenger system:
phosphorylation second messenger systems
Phosphorylation & Second Messenger Systems
  • Involves both allosteric & cov’ly mod’d enzymes
  • “First messenger” = non-lipid hormone
    • Binds cell membr receptor
    • Book ex: epinephrine
slide50
 Conform’l changes in membr-bound proteins
    • Receptor, G-proteins, adenylyl cyclase
    • All are allosteric prot’s
slide52
 Act’n adenylyl cyclase
    • Cat’s rxn ATP  cAMP
  • cAMP (what type of molecule?)
    • “Second signal”
    • Regulates activities of many enzymes
    • Act’s (usually) regulatory enz’s through allosteric control
slide53
Protein kinase A
    • 4 subunits (2 regulatory, 2 catalytic)
    • cAMP  binding of cAMP to regulatory units
    •  Allosteric change
    •  Catalytic subunits dissociate
    •  Catalytic subunits activated
slide54
For glycogen phosphorylase example:
    • PKA subunit dissociation
    •  Activation of PKA
    •  Phosph’n glycogen phosphorylase b
    •  Activation glycogen phosphorylase (now “a” form)
  • “Signal transduction cascade” = amplification of signal
slide56
PKA regulates many enzymes
  • cAMP regulates many pathways
    • Metabolic, others
slide58
Caffeine (methylated purine) inhibits breakdown of cAMP
    • What type of inhibitor might it be?
    • What pharmacologic effects would you expect from caffeine?