Nonenzymatic Protein Function And Protein Analysis Flashcards
structural proteins
compose the cytoskeleton, anchoring proteins, and much of the extracellular matrix
most common: collagen, elastin, keratin, actin, tubulin
generally fibrous in nature
motor proteins
have one or more heads capable of force generation through a conformational change
have catalytic activity, acting as Atlases to power movement
muscle contraction, vesicle movement within cells, and cell motility are most common applications
common ex: myosin, kinesin, dynein
binding proteins
bind a specific substrate, either to sequester it in the body or hold its concentration at a steady rate
cell adhesion molecules (CAMs)
allow cells to bind to other cells or surfaces
cadherins, integrins, selectins
cadherins
calcium-dependent glycoproteins that hold similar cells together
integrins
have two membrane-spanning chains and permit cells to adhere to proteins in the extracellular matrix
some also have signaling abilities
selectins
allow cells to adhere to carbohydrates on the surfaces of other cells and are most commonly used in the immune system
antibodies (immunoglobulins, Ig)
used by the immune system to target a specific antigen
contain a constant region and variable region; the variable region is responsible for antigen binding
two identical heavy chains and two identical light chains form a single antibody; they are held together by disulfide linkages and noncovalent interactions
antigen
may be a protein on the surface of a pathogen (invading organism) or toxin
ion channels
can be used for regulating ion flow into or out of a cell
three main types: ungated, voltage-gated, ligand-gated
ungated channels
ion channels that are always open
voltage-gated channels
ion channels that are open within a range of membrane potentials
ligand-gated channels
ion channels that open in the presence of a specific binding substance, usually a hormone or neurotransmitter
enzyme-linked receptors
participate in cell signaling through extracellular ligand binding and initiation of second messenger cascades
G-protein coupled receptors
have a membrane-bound protein associated with a trimeric G protein
also initiate second messenger systems
1. ligand binding engages the G protein
2. GDP is replaced with GTP; the α subunit dissociates from ß and γ subunits
3. the activated α subunit alters the activity of adenylate cyclase or phospholipase C
4. GTP is dephosphorylated to GDP; the α subunit rebinds to the ß and γ subunits
electrophoresis
uses a gel matrix to observe the migration of proteins in response to an electric field
native PAGE
maintains the protein’s shape, but results are difficult to compare because the mass-to-charge ratio differs for each protein
SDS-PAGE
denatures the proteins and masks the native charge so that comparison of size is more accurate, but the functional protein cannot be recaptured from the gel
isoelectric focusing
separates proteins by their pI; the protein migrates toward an electrode until it reaches a region of the gel where pH=pI of the protein
chromatography
separates protein mixtures on the basis of their affinity for a stationary phase or mobile phase
column chromatography
uses beads of a polar compound, like silica or alumina (stationary phase), with a non polar solvent (mobile phase)
ion-exchange chromatography
uses a charged column and a variably saline fluent
size-exclusion chromatography
relies on porous beads
larger molecules elute first because they are not trapped in the small pores
affinity chromatography
uses a bound receptor or ligand and an fluent with free ligand or a receptor for the protein of interest
X-ray crystallography
method of determining protein structure after protein is isolated
NMR can also be used
Edman degradation
determines amino acid sequencing through sequential degradation
Bradford protein assay
determine protein concentration
uses a color change from brown-green to blue to test for protein
most common
