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. Author manuscript; available in PMC: 2017 Jul 6.
Published in final edited form as: Annu Rev Biophys. 2015;44:311–337. doi: 10.1146/annurev-biophys-051013-023008

Table 1.

Membrane proteins of known structure with non-symmetrical or two-fold symmetrical folds

Order None 2-fold
Axis Perpendicular Planar
Group C2 c pC2 d aC2 pC2 22
Receptor, Enzyme YidC, TatC, OST, proteases, RTK, sulfur-transferase, cyt c ox aa3, cyt c1, PS-II SR-II, class C GPCR, glycophorin A BR, PRC, complex I, thiol oxidase, rhodopsin, UbiA prenyl-transferase
a Primary P-type ATPase ABC Export, ABC Import I, ABC Import II ABC export, ABC Import I ABC Import II1
b Second-ary CDF, MFS, APC, EIIC, DASS, CLC MATE, MFS, RND1 SMR CLC, APC,NPA1, CaCA,EAAT CNT,DASS, MFS,NCS2 Mrp1
Channel BcsA, PorA1 MgtE, SKT MIP, Amt, SecY, FNT, UT, TMBIM

Protein families (or one subunit of a larger complex) are organized by symmetry order, axis orientation (perpendicular or parallel to the membrane) and symmetry group. Bold indicates a regulatory role (e.g. stability, cooperativity).

a

Primary transporters,

b

secondary transporters.

c

pC2 indicates pseudo-C2 axis,

d

asymmetry. Italics indicates that the corresponding symmetry axis runs through the helices of the two repeats (interdigitating repeats). Blue text indicates asymmetry (synonymous with homo-oligomer, while pseudo-symmetry includes both hetero-oligomers or internal repeats).

1

Indicates symmetry is within a protomer in an oligomeric complex.

Abbreviations not in main text: PS-II, photosynthetic reaction center II; CDC, cholesterol-dependent cytolysin; CNT, concentrative nucleoside transporter; DEG-eNaC, degenerin epithelial sodium channel family; BR, bacteriorhodopsin; SR-II, sensory rhodopsin II; DASS, divalent anion:Na+ symporters.