Question

The following is a portion of the amino acid sequence of human GLUT1 purified from red blood cells.  Glucose is also shown for your convenience.

147  151 161   171   181

vspt alrgalgtlh qlgivvqili aqvfgldsim gnkd

A.  An internal 23 amino acid region of the sequence above is the 5th transmembrane domain of GLUT1.  The beginning of the sequence is an intracellular loop.  The end of the sequence is an extracellular loop.  Indicate where these regions might be in the sequence.  Explain how you derived at your hypothesis. What secondary structure might this transmembrane region be?  The mammalian membrane is 30 angstroms thick.  

B. The gray shaded residues in the above sequence represent the glucose binding domain of the 5th transmembrane region.  The glutamine at position 161 interacts with the substituent on C-4 of glucose.  How might Q161 it do this?  If you discovered that the glucose binding domains transmembrane regions 7, 8 and 10 in GLUT1 also contain a prevalence of threonine, serine, glutamine, and asparagine, would you be surprised?  How is it that amino acids not next to each other in the primary sequence in transmembrane region 5 (in gray) form a functional protein domain? What is the likely orientation of these transmembrane regions 5, 7, 8 and 10 in the membrane itself and why are they set up this way?

C.  One of the following plots represents a portion of GLUT1, one a porin (which is a transmembrane protein that is comprised of a b-barrel), and the other a cytosolic protein.  Can you know which plot represents which protein and why?

D. The V_max of a glucose transport into a certain preparation of red blood cells is determined to be 1206nmol glucose/s without ATP present in the buffer.  The V_max of a glucose transport into the same preparation of red blood cells is determined to be 1158nmol/s when ATP is present in the buffer.  However, when cells that do not express any glucose transporter are probed for rate of glucose transport, V_max is infinite.   Explain these data.  

Answer 1

And:- Plot c represents the portion porin as it shows highly hydropathy index As transmembrane proteins mostly contain hydrophobic residues and higher the hydropatty index, the more chydrophobic the amino acid therefore plot c represuts posion -Plot a represents the cytosotic portion as most of the residues have lower hydropathy endes which means they are hydrophillic