TABLE 1.

Susceptibility of GLUT1 side chains to proteolytic attack

Grouping and regiona	Potential sitesb	Sites cleavedc	Cleavage rated	SSRe
			%
1
TM1	7	4	57	38.7
TM7	10	6	60	55.1
TM2	9	4	44	65.8
TM8	5	2	40	45.8
TM3	13	1	8	68.1
TM9	12	0	0	65.5
TM4	9	4	44	59.5
TM10	11	1	9	76.3
TM5	7	2	29	56.8
TM11	8	2	25	46.4
TM6	9	0	0	81.4
TM12	12	0	0	101.4
2
Group 1 TMs (1, 4, 7, and 10)	37	15	41	57.4
Group 2 TMs (2, 5, 8, and 11)	29	10	34	53.7
Group 3 TMs (3, 6, 9, and 12)	46	1	2	79.1
3
N terminus	10	5	50
L1–2	10	7	70	44.1
L6–7	37	24	65	54.1
C terminus	19	10	53	37.5
Others	46	13	28
Total	122	59	48
4
Membrane	112	26	23
Extramembrane	122	59	48
5
GLUT1 total	234	85	36

^aRegions are delineated as 1) individual, membrane-embedded α-helices; 2) membrane-spanning helix groups; 3) loop, tail, and regions not embedded within the membrane; 4) summation of the individual membrane-embedded α-helices versus all other regions; and 5) the proteolytic susceptibility of the entire transport structure

^bThe potential number of cleavage sites

^cThe number of sites detected as cleavage sites

^dThe percent accessibility of the region to proteolysis

^eThe relative hydrophobicity of each region was calculated using the sequence specific retention (SSR) calculator developed by the Manitoba Center for Proteomics (42). For membrane-spanning α-helices, this calculation covers only peptide sequence that is embedded in the bilayer domain according to Salas-Burgos et al. (11) (Fig. 1)