Modular structure of proteins Flashcards
What is a structural motif
A minimum arrangement of independently forming secondary structures combining recognisable folds across many different proteins
How does a motif and domain differ
A domain more clearly defines a functional unit
How are motifs and domains similar
both are modular in nature and both are evolutionarily conserved
What is a domain
A complex structure at the tertiary or quaternary level, often involving interaction between distant parts of a protein or motifs
EF hand motif
Calcium binding motif
Resembles a helix turn helix with a metal ion such as calcium that stabilises the overall structure
Calmodulin has 4 EF hand motifs
Greek key motif
Consists of antiparallel beta strands that generally isnt associated with a specific function
Beta barrel motif
Beta strands forming beta sheets which are wrapped around to form a circular tunnel
Beta-alpha-beta motif
Two parallel strands of a beta sheet interlinked with an alpha helix
What are DNA binding motifs
They are helices which can be inserted into the major groove of DNA, often dimerise creating a a larger and more complex DNA binding domain
What is a membrane bound receptor domain
Bundles of alpha helices or beta sheets
What is the extracellular region
ligand binding domain
What is the transmembrane region
Domain that anchors the protein to the membrane and embeds it into the lipid bilayer
What is the intracellular region
Domain that interacts with the interior of the cell or organelle relaying the signal
What does domain shuffling achieve
Results in modular units of function being evolutionarily conserved
Helix-loop-helix motif structure and function
- DNA binding motif in the dimeric form
- Central portion formed from overlapping helices that allow for dimerisation
- Terminal parts contain basic amino acids that interact with the positively charged major groove of DNA
What is the advantage of helix-loop-helix motifs being able to form heterodimers
Extends the functionality of individual proteins as different monomers can join together allowing the regulation of different genes in different ways in response to different stimuli
Leucine zipper motif structure
Formed from 2 contiguous alpha helices, the dimers zip together forming a coil a the top
The coil is held together by hydrophobic interactions down opposing sides of the helix
The basic amino acids are also on the lower part of the helix
Helix-turn-helix structure
Consists of two short helices oriented at right angles to each others and connected by a ‘turn’
Where are H-T-H found
In eukaryotic and prokaryotic DNA binding poteins e.g. CRO repressor and homebox proteins
What does the CRO repressor do
Recognises palindromic sequences and binding to the DNA it represses transcription
Zinc finger motif
It is an alpha helix and a beta sheet held together by non-covalent interactions with zinc
Where do you find zinc finger motive
In manu ornate receptors e.g. glucocorticoid, mineralocorticoid, oestrogen, progesterone and vit D receptors
