lecture 7 Flashcards
the twist angle
between beta strands, forms the beta sheet
Why are beta sheets so stable?
hydrogen bonds (and the cumulative strength of them)
protein domains definition
distinct structural units, separate functions, fold independently and as compact units
protein domains can
move as a single entity w respect to entire protein
How many protein domains does a protein have?
they may have one or more.
each domain is usually made of a single stretch of primary sequence
Src Protein kinase
has 4 functional domains, diff functions
this is one protein
intrinsically disordered sequences functional importance
binding
tethering
scaffolding
flexibility
tertiary structure of protein stabilized by
non covalent interactions
(usually between R groups or R groups and backbones)
noncovalent interactions (4)
help proteins fold and maintain shape
1. h bonds
2. electrostatic interactions
3. van der waals
4. hydrophobic interactions
Cysteine can
stabilize proteins through covalent interactions. (disulfide bonds)
cysteine-cysteine
or
cycteine-polypeptide
Backbone model
shows the backbone
ribbon model
shows the backbone and emphasizes the secondary structure
wire model
shows the backbone and side chains
space-filling model
contour map of the surface
proteins have different shapes
structure and function are closely related
two major groups of proteins
fibrous proteins
globular proteins
fibrous proteins
-dominated by a single repeating element of secondary structure
-has properties that give strength/flexibility
ex. alpha keratin and silk, elastin, collagen
globular proteins
-spherical, often contain several types of secondary structure
ex. myoglobin, lysozyme, cytochrome c
alpha keratin (fibrous)
right handed alpha helix
coil composed of two alpha keritin chains that is left handed
silk (fibrous proteins)
anitparallel beta strands held together by H bonds to form beta sheets
small R groups
Fibroin in silk is rich in Ala and Gly– why?
allows the close packing of beta sheets and interlocking arrangement of R groups
Globular proteins structural diversity
for diverse functions:
enzymes, motor proteins regulatory proteins etc.
native state of the protein
usually the most stable (lowest energy) state of the folded protein
chaperone proteins
help the folding process of proteins
misfolded proteins can form
large aggregates, affecting cellular functions
Anfinsen dogma
3D structure of a protein is determined only by its protein’s amino acid sequence
Not true for all proteins!!!
Chris Anfinsen Refolding Experiment
Some denatured proteins will spontaneously refold in vitro
Anfinsen’s Refolding experiment is not true for all proteins
-generally only true for small proteins
-some must fold during protein synthesis
-some need the help of chaperones
Some proteins contain more than one
polypeptide chain
each polypeptide chain is called a
subunit
CAP protein structure
quaternary structure
composed of two identical subunits
Hemoglobin structure
quaternary structure
composed if two identical alpha subunits and two identical beta subunits
proteins can be classified into
protein families where each member has an amino acid sequence and 3D conformation that closely resembles eachother
ex. Elastase and chymotrypsin
-they are similar but w different substrate specificity
Substrate specificity: Elastase
Ala, Val, Gly
Substrate specificity: Chymotrypsin
Tyr, Phe, Trp
protein assembly
proteins can spontaneously self assemble!
all info needed for self assembly is in the macromolecule itself
proteins can form large assemblies such as
filaments, sheets, or spheres made up of many subunits bound to eachother
