Post on 07-Apr-2018
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Protein Structure
From: Protein Data Bank PDB ID: 1B0EKalus, W., Zweckstetter, M., Renner, C., Sanchez, Y., Georgescu, J., Grol, M., Demuth, D., Schumacher, R., Dony, C., Lang, K., Holak, T. A.: structure of the IGF-binding
domain of the insulin-like growth factor-binding protein-5 (IGFBP-5): implications for IGF and IGF-I receptor interactions.EMBO J17pp. 6558 (1998)
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Functions
Diverse functions related to structure Structural components of cells
Motor proteins
Enzymes
Antibodies
Hormones Hemoglobin/myoglobin
Transport proteins in blood
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Structure
Amino acids
Amino group(NH2)
Carboxyl group
(COOH)
From: Elliott, WH. Elliott, DC. (1997) Biochemistry
and Molecular Biology. Oxford: Oxford University
Press. p23
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Amino acids
20 amino acids makeup protein
8 essential aminoacids
9 in infant (histidine)
Dipolar +ve end (NH3
+)
-ve end (COO-)
From: Elliott, WH. Elliott, DC. (1997) Biochemistry
and Molecular Biology. Oxford: Oxford UniversityPress. p23
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Protein structure - bonding
5 bonds or forces determine structure
Peptide bond Hydrogen bond
Disulfide bond
Ionic bond Hydrophobic force
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Peptide bond
Peptide bond joinsamino acids
Bond at both ends Increases range of
possible proteins 2 peptides can result
from bonding of 2
amino acids 1.0 x 1026 peptides can
be formed from 20amino acids
From: Elliott, WH. Elliott, DC. (1997) Biochemistry
and Molecular Biology. Oxford: Oxford University
Press. p23
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Primary protein structure
Linear sequence of
amino acids formsprimary structure
Sequence essential for
proper physiologicalfunction
Bettelheim & March (1990) Introduction
to Organic & Biochemistry
(International Edition) Philadelphia:Saunders College Publishing, p299
Primary structure of insulin
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Sickle cell anemia
Replacement of
single glutamine
with valine in one
polypeptide chain
of hemoglobinalters structure
and function Bettelheim & March (1990) Introduction to Organic & Biochemistry(International Edition) Philadelphia: Saunders College Publishing, p301
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Secondary protein structure
Peptide chains fold into secondary
structures: - helix
- pleated sheet
Random coil
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- helix
Shapemaintained by
hydrogen bondsbetween C=Oand N-H groupsin backbone
R groupsdirectedoutward from
coil
From: Elliott, WH. Elliott, DC. (1997) Biochemistry and Molecular
Biology. Oxford: Oxford University Press. p28
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- pleated sheet
Structuremaintained by
hydrogen bondsbetween C=O andN-H groups in
backbone R groups directed
above and below
backboneFrom: Elliott, WH. Elliott, DC. (1997) Biochemistry and Molecular
Biology. Oxford: Oxford University Press. p29
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Random coil Not really random
structure, just non-repeating
Random coil has fixedstructure within a givenprotein
Commonly calledconnecting loop region
Structure determinedby bonding of sidechains (i.e. notnecessarily hydrogenbonds)
From: Elliott, WH. Elliott, DC. (1997) Biochemistry
and Molecular Biology. Oxford: Oxford University
Press. p27
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Tertiary protein structure
Secondary structures fold and pack
together to form tertiary structure
Usually globular shape
Tertiary structure stabilised by bondsbetween R groups (i.e. sidechains)
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H bonds weak
allowing to be
broken and
reformed easily
Allows structural
change produces
functional
molecules
Hydrogen bond
Tertiary structure - H bond
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Tertiary structure - disulfidebond
Covalent bondbetween sulfuratoms on twocysteine amino
acids
From: Elliott, WH. Elliott, DC. (1997) Biochemistry
and Molecular Biology. Oxford: Oxford University
Press. p32
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Tertiary structure - ionic bond
Ions on Rgroups formsalt bridgesthrough ionic
bonds
From: Summerlin, LR. (1981) Chemistry for the Life Sciences. New
York: Random House, p459
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Tertiary structure -hydrophobic forces
Close attraction of non-
polar R groups through
dispersion forces
Very weak but collective
interactions over large
area stabilise structure
Repel polar and charged
molecules/particles Bettelheim & March (1990) Introduction to Organic & Biochemistry(International Edition) Philadelphia: Saunders College Publishing, p302
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Quaternary protein structure
Arrangement of
multiple tertiary
structures into single
functional complex
Allows for changes in
structure/function in
response to chemical
stimuliFrom: Elliott, WH. Elliott, DC. (1997) Biochemistry and
Molecular Biology. Oxford: Oxford University Press. p27