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Types of Transmembrane Proteins

Transmembrane proteins span entire biological membrane. They are also called as integral proteins because they run throughout the biomembrane. The firm attachment of Integral proteins to membranes is actually the result of hydrophobic interaction between membrane lipids and hydrophobic domains of the protein.
There are 2 types of transmembrane proteins
Alpha Helical: Present in inner membranes of bacterial cells or plasma membranes of eukaryotes. This is the major category of transmembrane proteins
Beta Barrels: Found only in outer membranes of Gram Negative Bacteria, cell wall of Gram Positive Bacteria, and outer membranes of mitochondria and chloroplast.
Another classification refers to the position of the N- and C-terminal domains.
Types I and II have only one transmembrane helix; the amino-terminal domain is outside the cell in type I proteins and inside in type II.
Type III proteins have multiple transmembrane helices in a single polypeptide.
In type IV proteins, transmembrane domains of several different polypeptides assemble to form a channel through the membrane.
Type V proteins are held to the bilayer primarily by covalently linked lipids
Type VI proteins have both transmembrane helices and lipid (GPI) anchors.
Reference: Lehninger Principles of Biochemistry 4 edition
Single Pass transmembrane protein: These allow only one component to pass through the membrane. This single-pass transmembrane protein has an extracellular N-terminus and cytoplasmic C-terminus for a cell membrane.
Multipass transmembrane protein: Multipass transmembrane protein basically allows more than one ion or molecule to pass through the membrane protein. In this protein the polypeptide crosses the lipid bilayer multiple times. Most of the membrane-spanning segments of polypeptide chains are thought to have an alpha helical conformation. This is because in a lipid environment the hydrogen bonding between peptide bonds would be maximized if the polypeptide chain were to form a regular alpha-helix

Find two examples of each transmembrane protein shown in this picture. Preferably your two choices should come from vastly different species for example (glutamate receptors in plants and mouse maybe (Arabidopsis thalia and Mus musculus)
A single transmembrane alpha-helix:
Human glycophorin A (GpA): Glycophorin is a glycoprotein of the erythrocyte plasma membrane, where 60% of the mass consists of complex oligosaccharide units are covalently attached to specific amino acid residues. Ser, Thr, and Asn residues are the most common points of attachment
Human Growth Hormone Receptors
Other examples include G-protein linked receptors, insulin receptors, Receptor Tyrosine kinase.
A polytopic alpha-helical protein:
Bacteriorhodopsin (PDB ID 2AT9): The single polypeptide chain folds into seven hydrophobic alpha helices, each of which traverses the lipid bilayer roughly perpendicular to the plane of the membrane. The seven transmembrane helices are clustered, and the space around and between them is filled with the acyl chains of membrane lipids. The light-absorbing pigment retinal is buried deep in the membrane in contact with several of the helical segments. It is light driven proton pump densely packed in regular arrays in purple membrane of the bacterium Halobacterium salinarum.
Reference: Lehninger Principles of Biochemistry 4th edition
Prominin: a novel microvilli-specific polytopic membrane protein of the apical surface of epithelial cells. It is targeted to plasma membrane protrusions of non-epithelial cells. It is a membrane associated 15Kda protein.(Reference: Anja Weigmann*, Denis Corbeil*, Andrea Hellwig, and Wieland B. Huttner†PNAS November 11, 1997 vol. 94 no. 23 12425-12430)
A transmembrane Beta barrel:
a) The Staphylococcus aureus alpha-hemolysin toxin (PDB ID 7AHL) is composed of seven identical subunits, each contributing one hairpin-shaped pair of beta strands to the 14-stranded barrel.
b) E.coli outer membrane protein TolC (PDB ID 1EK9) central to multidrug efflux and protein export. It is a transporter molecule, has three separate subunits, each contributing four beta strands in this 12-stranded barrel.
Other examples are:
Maltoporin (PDB ID 1MAL)

Impact of Climate Change on Moose Population

Moose in the Noose?
From Montana to Minnesota, Ontario and Wyoming to Hew Hampshire moose numbers are in steep decline. Could climate change be to blame?
These majestic animals, which can be over 6 feet tall and weigh 700 kg, are a highlight for wildlife enthusiasts visiting America’s northern states and bring in much needed revenue for local communities. They are also important components of the boreal forest ecosystem. Unfortunately these mostly solitary creatures are becoming increasingly more difficult to find by hunters and scientists alike.
Moose number declines
40% drop in the number of hunting tags released
Down 70% since 2006
New Hampshire
Dropped from 7000 to 4600
70% drop since 1998

Montana Mystery
Dwindling populations in Montana have left local people worried and scientists scratching their heads as to why. Currently moose numbers in Montana are not checked regularly, instead they rely on anecdotal evidence from biologists and hunters as to what the situation on the ground is. But many people are worried. Nick DeCesare, the biologist leading the study said “There’s fewer moose out there, and hunters are working harder to find them.” So worried are they that the Montana Fish, Wildlife