Download Powerpoint Presentation: Proteins

PROTEINS
FOLDED POLYPEPTIDES
© 2007 Paul Billiet ODWS
PRIMARY STRUCTURE
The sequence of amino acids
MIL1 sequence:
>gi|7662506|ref|NP_056182.1| MIL1 protein [Homo sapiens]
MEDCLAHLGEKVSQELKEPLHKALQMLLSQPVTYQAFRECTLETTVHASGWNKILVPLVLLRQML
LELTRLGQEPLSALLQFGVTYLEDYSAEYIIQQGGWGTVFSLESEEEEYPGITAEDSNDIYILPS
DNSGQVSPPESPTVTTSWQSESLPVSLSASQSWHTESLPVSLGPESWQQIAMDPEEVKSLDSNGA
GEKSENNSSNSDIVHVEKEEVPEGMEEAAVASVVLPARELQEALPEAPAPLLPHITATSLLGTRE
PDTEVITVEKSSPATSLFVELDEEEVKAATTEPTEVEEVVPALEPTETLLSEKEINAREESLVEE
LSPASEKKPVPPSEGKSRLSPAGEMKPMPLSEGKSILLFGGAAAVAILAVAIGVALALRKK
length: 386amino acids
© Anne-Marie Ternes
PRIMARY STRUCTURE
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The numbers of amino acids vary
(e.g. insulin 51, lysozyme 129, haemoglobin
574, gamma globulin 1250)
The primary structure determines the folding of
the polypeptide to give a functional protein
Polar amino acids (acidic, basic and neutral)
are hydrophilic and tend to be placed on the
outside of the protein.
Non-polar (hydrophobic) amino acids tend to be
placed on the inside of the protein
© 2007 Paul Billiet ODWS
Infinite variety
The number of possible sequences is
infinite
An average protein has 300 amino acids,
At each position there could be one of 20
different amino acids
= 10390 possible combinations
 Most are useless
Natural selection picks out the best
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© 2007 Paul Billiet ODWS
SECONDARY STRUCTURE
The folding of the N-CC backbone of the
polypeptide chain
using weak hydrogen
bonds
© Text 2007 Paul Billiet ODWS
© Science Student
SECONDARY STRUCTURE
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This produces the alpha helix and beta pleating
The length of the helix or pleat is determined by certain
amino acids that will not participate in these structures
(e.g. proline)
© Text2007 Paul Billiet ODWS
© Dr Gary Kaiser
TERTIARY STRUCTURE
The folding of the polypeptide into
domains whose chemical properties are
determined by the amino acids in the
chain
MIL1 protein
© 2007 Paul Billiet ODWS
© Anne-Marie Ternes
TERTIARY STRUCTURE
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This folding is sometimes held together by
strong covalent bonds
(e.g. cysteine-cysteine disulphide bridge)
Bending of the chain takes place at certain
amino acids
(e.g. proline)
Hydrophobic amino acids tend to arrange
themselves inside the molecule
Hydrophilic amino acids arrange themselves
on the outside
© 2007 Paul Billiet ODWS
Chain B of Protein Kinase C
© Max Planck Institute for Molecular Genetics
QUATERNARY STRUCTURE
Some proteins are
made of several
polypeptide subunits
(e.g. haemoglobin has
four)
Protein Kinase C
© Max Planck Institute for Molecular Genetics
© Text 2007 Paul Billiet ODWS
QUATERNARY STRUCTURE
These subunits fit together to form the
functional protein
 Therefore, the sequence of the amino
acids in the primary structure will influence
the protein's structure at two, three or
more levels
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© 2007 Paul Billiet ODWS
Result
Protein structure depends upon the
amino acid sequence
This, in turn, depends upon the sequence
of bases in the gene
© 2007 Paul Billiet ODWS
PROTEIN FUNCTIONS
Protein structure determines protein
function
 Denaturation or inhibition which may
change protein structure will change its
function
 Coenzymes and cofactors in general may
enhance the protein's structure
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© 2007 Paul Billiet ODWS
Fibrous proteins
Involved in structure: tendons ligaments
blood clots
(e.g. collagen and keratin)
 Contractile proteins in movement: muscle,
microtubules
(cytoskelton, mitotic spindle, cilia, flagella)
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© 2007 Paul Billiet ODWS
Globular proteins
most proteins which move around (e.g.
albumen, casein in milk)
 Proteins with binding sites:
enzymes, haemoglobin, immunoglobulins,
membrane receptor sites
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© 2007 Paul Billiet ODWS
Proteins classified by function
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CATALYTIC: enzymes
STORAGE: ovalbumen (in eggs), casein (in milk), zein
(in maize)
TRANSPORT: haemoglobin
COMMUNICATION: hormones (eg insulin) and
neurotransmitters
CONTRACTILE: actin, myosin, dynein (in microtubules)
PROTECTIVE: Immunoglobulin, fibrinogen, blood
clotting factors
TOXINS: snake venom
STRUCTURAL: cell membrane proteins, keratin (hair),
collagen
© 2007 Paul Billiet ODWS