Transcript Protein Structure and Function Lecture 4

Lecture 4-Kumar
Protein Structure and Function
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Peptide Bond Is Rigid and Planar
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Terminology
• Conformation – spatial arrangement of
atoms in a protein
• Native conformation – conformation of
functional protein
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Alpha Helix
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Beta-Sheets
• Beta-sheets
formed from
multiple side-byside beta-strands.
• Can be in parallel or
anti-parallel
configuration
• Anti-parallel betasheets more stable
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Bonds holding the tertiary structure of
Proteins
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Protein Function
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Catalysis – enzymes
Structural – keratin
Transport – hemoglobin
Trans-membrane transport – Na+/K+ ATPases
Toxins – rattle snake venom, ricin
Contractile function – actin, myosin
Hormones – insulin
Storage Proteins – seeds and eggs
Defensive proteins – antibodies
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Protein Classification
• One polypeptide chain - monomeric protein
• More than one - multimeric protein
Homomultimer – all one kind of chain
Heteromultimer - two or more different chains
(e.g. Hemoglobin is a heterotetramer. It has two alpha
chains and two beta chains).
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Protein Classification
Fibrous –
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polypeptides arranged in long strands or
sheets
water insoluble (lots of hydrophobic AA’s)
strong but flexible
Structural (keratin, collagen)
Globular
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polypeptide chains folded into spherical or
globular form
water soluble
contain several types of secondary structure
diverse functions (enzymes, regulatory
proteins)
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Protein Classification
• Simple – composed only of amino acid residues
• Conjugated – contain prosthetic groups
(metal ions, co-factors, lipids, carbohydrates)
Example: Hemoglobin – Heme
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Diseases caused by changes in protein structure
• spongiform encephalopathy (BSE or mad cow disease) seen
in cattle and livestock and Creutzfeldt-Jakob disease (CJD)
seen in humans.
• Sickle Cell Anemia – single amino acid change in hemoglobin
related to disease
• Osteoarthritis – single amino acid change in collagen protein
causes joint damage
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Prion Misfolding
Prion protein misfolding
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Prion propagation
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Sickle cell anemia
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Mutations in a- or b-globin
genes can cause disease state
• Sickle cell anemia – E6 to
V6
• Causes V6 to bind to
hydrophobic pocket in
deoxy-Hb
• Polymerizes to form long
filaments
• Cause sickling of cells
• Sickle cell trait offers
advantage against malaria
• Fragile sickle cells can not
support parasite
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Learning objectives-protein structure and
function
• Know the definitions of primary, secondary, tertiary, and
quaternary structures or protein
• Understand the differences between globular and fibrous
proteins
• Know the forces that stabilize these structures
• Understand the type of bonds that stabilize these structures
• Understand that certain changes in protein structure can
change the structure and function of protein
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