Table 2.

Mutagenesis Studies of BCRP

Mutation	Position in BCRP	Effect	Reference
Natural variants
V12Ma	N-terminus	No major effect on membrane expression and function	[114, 120–121]
G51Ca	N-terminus	No major effect on membrane expression and function	[120]
Q141Ka	NBD	Lower protein expression and transport activity	[112, 114, 121]
T153M, Q166E, I206La	NBD	No major effect on expression and function	[120, 137]
Q126stop, F208S, E334stopa	NBD	No expression and transport activity	[120]
S248Pa	NBD	Well expressed, but with no transport activity	[120]
F489La	TM3	Well expressed, no transport activity for porphyrin and methotrexate	[120]
F571Ia	TM5	Well expressed, slightly decreased activity depending on substrates	[120]
N590Y, D620Na	Extracellular loop 3	Well expressed, slightly decreased activity depending on substrates	[120, 137]
Artificial mutants
K86M, K86I	NBD, Walker A	No transport or ATPase activity, but ATP binding retained No transport or ATPase activity, altered subcellular expression	[70] [138]
E211Q	NBD, Walker B	Completely abolished ATPase and transport activity	[124]
The 315–316 deletion	NBD	Impaired BXP-21 antibody recognition, but with no effect on function	[139]
R383A, R383G	Linker region	Increased protein degradation and decreased protein strability Altered subcellular distribution and glycosylation	[126]
T402A, T402L, T402R	TM1	Well expressed, impaired transport activity	[97], b
G406L, G410L, G406L/G410L	GXXXG motif in TM1	Well expressed, impaired transport and ATPase activity	[127]
N418Q	Extracellular loop 1	Well expressed, not a N-linked glycosylation site	[92]
R426A	Extracellular loop 1	Increased protein degradation and decreased protein stability	c
E446X	Extracellular loop 1	Well expressed, but with no drug resistance	[109]
K452A, H457A	TM2	Well expressed, increased transport activity and drug resistance	[105]
K453D, R465A	TM2	Well expressed, lower transport activity and drug resistance	[105]
K473A	Intracellular loop 1	Well expressed, no effect on transport activity and drug resistance	[105]
R482G, R482T, R482X	TM3	Well expressed, with altered substrate specificity. For example, “gain-of- function” for transport of daunorubicin and rhodamine 123; but completely lost transport activity for methotrexate	[106–109] [122, 140]
G553L, G553E	Intracellular loop 2	Impaired trafficking, expression, and N-linked glycosylation	[130]
L554P	Intracellular loop 2	Completely lost resistance to SN-38 and mitoxantrone	[76]
N557X	Intracellular loop 2	Lower resistance to SN-38 for N557H, N557D, and N557E Lower resistance to mitoxantrone for N557H, N557E, but not for N557D	[109]
N596Q	Extracellular loop 3	N-linked glycosylation site	[92–93]
C592A, C608A, C592A/C608A	Extracellular loop 3	Impaired expression and function for C592A and C608A Partially restored plasma membrane expression for C592A/C608A Transport of mitoxantrone was normal, but transport of BODIPY-prazosin was impaired for C592A/C608A	[82]
C592A/C603A/C608A	Extracellular loop 3	Decreased expression with no measurable activity	[82]
C603A, C608A	Extracellular loop 3	Involved in BCRP dimerization	[86]
C603A	Extracellular loop 3	No effect on membrane expression and function; disulfide bridge	[82–84]
		No effect on membrane expression, function and dimerization in vivo	[80]
C592S, C603S, C608S	Extracellular loop 3	Impaired expression and function	[86]
C592S/C603S/C608S	Extracellular loop 3	Impaired expression and subcellular localization. Retained significant activity with alteration in substrate specificity	[86]
H630X	TM6	No major effect on drug resistance	[109]
Cys-less BCRP		Well expressed in Sf9 cells, but with no transport activity	[85]

^aThe natural variants of BCRP are illustrated in italics. The allele frequencies of individual single nucleotide polymorphisms among different ethnic groups have been detailed in references [120, 141];

^bNi et al., manuscript submitted;

^cUnpublished results. NBD, nucleotide binding domain. TM, transmembrane α-helix. Positions of the residues in BCRP are based on the membrane topology illustrated in Fig. 3.