Table 1.

Arsenic-binding proteins in MCF-7 cells identified by MALDI-MS

Name	MW (Da)	Total score1	No. of Peptides matched	Function
Tubulin β2 2	49,799	990	33	Structural subunit of microtubules
Tubulin β5 2	49,639	974	40	Structural subunit of microtubules
Hsp 90β 3	83,081	961	25	Stress response
Pyruvate kinase M2 (PKM2)	57,746	723	19	Glycolysis
HnRNP K	50,944	644	27	Mitochondria-related protein
Phosphoglycerate kinase 1	44,568	599	13	Glycolysis
Pyruvate carboxylase	129,551	552	12	Glyconeogenesis and lipogenesis
Neural enolase	47,008	516	12	Glycolysis
β-tubulin 2	50,004	474	19	Structural subunit of microtubules
β-tubulin-1 2	41,465	465	15	Structural subunit of microtubules
Transketolase	67,835	425	16	Pentose phosphate cycle
D-3-phosphoglycerate dehydrogenase	56,614	419	7	Amino acid biosynthesis
β-actin 2	41,648	397	14	Cytoskeleton
Malate dehydrogenase	35,509	360	9	Tricarboxylic acid cycle
Ubiquitin-activating enzyme E1	117,774	321	8	Proteolysis
6-phosphogluconate dehydrogenase	52,975	319	9	Pentose phosphate cycle
Filamin A	280,586	311	8	Cytoskeleton
T-complex protein 1, theta subunit	59,582	301	7	Stress response
Glyceraldehyde-3-phosphate dehydrogenase	35,899	258	8	Glycolysis
Importin 90	97,108	248	7	Nuclear import
Annexin II	38,449	226	5	Phospholipids-binding protein
Cytokeratin 2-1	65,847	216	4	Late cytoskeletal intermediate filament
Lactate dehydrogenase B chain	36,484	176	4	Glycolysis
ATP synthase alpha chain	59,714	174	3	Mitochondrial ATP synthesis
Hsp27 3	22,768	158	3	Stress response
Elongation factor 2	95,146	146	3	Protein biosynthesis
Puromycin-sensitive aminopeptidase	103,237	140	3	Aminopeptidase
HnRNP C1/2	33,667	137	3	Mitochondrial protein
Nucleolar protein p120	94,020	131	3	Ribonucleoprotein
GTP-binding nuclear protein RAN	24,408	122	3	Nucleocytoplasmic transport
Ribophorin I (glycosylation)	68,527	121	3	Protein amino acid glycosylation
DNA replication licensing factor MCM6	92,831	107	3	DNA replication
Eukaryotic translation initiation factor 4A1/2	46,125	99	3	Protein translation
Protein disulfide isomerase precursor 2	57,081	97	3	Stress response
ATP-AMP transphosphorylase 2	26,330	71	3	Adenylate kinase
Proteasome subunit alpha type 6	27,382	70	3	Proteolysis
Rho GDP-dissociation inhibitor 1	23,193	56	3	GDP/GTP exchange
Triosephosphate isomerase	26,522	140	2	Isomerase
Clathrin heavy chain 1	191,493	112	2	Coated pits and vesicles
Methylcrotonyl-CoA carboxylase alpha chain	80,382	102	2	Leucine catabolism
14-3-3 protein tau	27,747	105	2	Adapter protein
Tumor rejection antigen 1 (GRP94) 3	92,411	94	2	Stress response
HnRNP A2/B1	37,407	90	2	Mitochondrial protein
Cytokeratin e2	65,825	84	2	Cytoskeleton
Elongation factor 1-delta	31,103	73	2	Protein biosynthesis
Palmitoyl-protein thioesterase	34,171	78	1	Protein modification
Alpha-actinin 4	104,788	76	1	F-actin cross-linking protein
Hsp70-4 3	94,240	49	1	Stress response
Peroxiredoxin 4 2	30,540	48	1	Redox regulation
T-complex protein 1, delta subunit	57,803	46	1	Stress response

¹Probability based Mowse score is −10*Log(P), where P is the probability that the observed match is a random event. Individual ions scores >45 indicate identity or extensive homology (p<0.05)(http://www.matrixscience.com/).

²Known arsenic-binding proteins (15, 25). Arsenic has been shown to bind peroxiredoxin-1 (thioredoxin peroxidase 2) (24). Its active site is the redox-active Cys⁵² oxidized to Cys-SOH. Cys-SOH rapidly reacts with Cys¹⁷³-SH of the other subunit to form an intermolecular disulfide with a concomitant homodimer formation. Similar to peroxiredoxin-1 in structure and function, peroxiredoxin-4 (thioredoxin peroxidase AO372) has its active site, the redox-active Cys¹²⁴, oxidized to Cys-SOH. Cys-SOH rapidly reacts with Cys²⁴⁵-SH of the other subunit to form an intermolecular disulfide with a concomitant homodimer formation.

³Stress response proteins known to be induced by arsenic treatment (37).