chapter 5 1 protein function reversible binding of protein to a ligand
Download
Skip this Video
Download Presentation
Chapter 5.1: Protein Function - Reversible Binding of Protein to a Ligand

Loading in 2 Seconds...

play fullscreen
1 / 26

Chapter 5.1: Protein Function - Reversible Binding of Protein to a Ligand - PowerPoint PPT Presentation


  • 203 Views
  • Uploaded on

Chapter 5.1: Protein Function - Reversible Binding of Protein to a Ligand. CHEM 7784 Biochemistry Professor Bensley. CHAPTER 5.1 Reversible Binding of Protein to a Ligand. Reversible binding of ligands Structure of myoglobin and hemoglobin Origin of cooperativity in hemoglobin.

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 ' Chapter 5.1: Protein Function - Reversible Binding of Protein to a Ligand' - thuong


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
chapter 5 1 protein function reversible binding of protein to a ligand

Chapter 5.1: Protein Function - Reversible Binding of Protein to a Ligand

CHEM 7784

Biochemistry

Professor Bensley

chapter 5 1 reversible binding of protein to a ligand
CHAPTER 5.1Reversible Binding of Protein to a Ligand
  • Reversible binding of ligands
  • Structure of myoglobin and hemoglobin
  • Origin of cooperativity in hemoglobin

Today’s Objectives - To learn and understand:

functions of globular proteins
Functions of Globular Proteins
  • Storage of ions and molecules
    • myoglobin, ferritin
  • Transport of ions and molecules
    • hemoglobin, serotonin transporter
  • Defense against pathogens
    • antibodies, cytokines
  • Muscle contraction
    • actin, myosin
  • Biological catalysis
    • chymotrypsin, lysozyme
binding quantitative description
Binding: Quantitative Description
  • Consider a process in which a ligand (L) binds reversibly to a site in the protein (P)
  • The equilibrium composition is characterized by the equilibrium constant Ka

ka

+

L

PL

P

kd

binding analysis in terms of the bound fraction
Binding: Analysis in Terms of the Bound Fraction
  • In practice, we can often determine the fraction of occupied binding sites
  • Substituting [PL] with Ka[L][P], we’ll eliminate [PL]
  • Eliminating [P] and rearranging gives the result in terms of equilibrium association constant:
  • In terms of the more commonly used equilibrium dissociation constant:
binding graphical analysis
Binding: Graphical Analysis
  • The fraction of bound sites depends on the free ligand concentration and Kd
  • In a typical experiment, ligand concentration is the known independent variable
  • Kd can be determined graphically or via least-squares regression

[L]  [L]total

specificity lock and key model
Specificity: Lock-and-Key Model
  • “Lock and Key” model by Emil Fischer (1894) assumes that complementary surfaces are preformed.

+

specificity induced fit
Specificity: Induced Fit
  • Conformational changes may occur upon ligand binding (Daniel Koshland in 1958).
    • This adaptation is called the inducedfit.
    • Induced fit allows for tighter binding of the ligand
    • Induced fit can increase the affinity of the protein for a second ligand
  • Both the ligand and the protein can change their conformations

+

myoglobin hemoglobin
Myoglobin/Hemoglobin
  • First protein structures determined
  • Oxygen carriers
  • Hemoglobin: transportsO2 from lungs to tissues
  • Myoglobin: O2storage protein
mb and hb subunits structurally similar
Mb and Hb Subunits Structurally Similar
  • 8 alpha-helices
  • Contain heme group
  • Mb monomeric protein
  • Hbheterotetramer (α2β2)

myoglobin

hemoglobin

oxygen binding curves
Oxygen Binding Curves
  • Mb has hyberbolic O2 binding curve
  • Mb binds O2 tightly. Releases at very low pO2
  • Hb has sigmoidal O2 binding curve
  • Hb high affinity for O2 at high pO2 (lungs)
  • Hb low affinity for O2 at low pO2 (tissues)
o 2 binding to hb shows positive cooperativity
O2 Binding to Hb shows Positive Cooperativity
  • Hb binds four O2 molecules
  • O2 affinity increases as each O2 molecule binds
  • Increased affinity due to conformation change
  • Deoxygenated form = T (tense) form = low affinity
  • Oxygenated form = R (relaxed) form = high affinity
allosteric interactions
Allosteric Interactions
  • Allosteric interaction occurs when specific molecules bind a protein and modulate activity
  • Allosteric modulators or allosteric effectors
  • Bind reversibly to site separate from functional binding or active site
  • Modulation of activity occurs through change in protein conformation
  • 2,3 bisphosphoglycerate (BPG), CO2 and protons are allosteric effectors of Hb binding of O2
ad