Nonequivalence of alpha-bungarotoxin binding sites in the native nicotinic receptor molecule

Journal Article · Tue Jan 30 00:00:00 EST 1990 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00456a029· OSTI ID:6746985

Conti-Tronconi, B M; Tang, F; Walgrave, S; Gallagher, W ^[1]

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1. Univ. of Minnesota, St. Paul (USA)

In the native, membrane-bound form of the nicotinic acetylcholine receptor (M-AcChR) the two sites for the cholinergic antagonist alpha-bungarotoxin (alpha-BGT) have different binding properties. One site has high affinity, and the M-AcChR/alpha-BGT complexes thus formed dissociate very slowly, similar to the complexes formed with detergent-solubilized AcChR (S-AcChR). The second site has much lower affinity (KD approximately 59 +/- 35 nM) and forms quickly reversible complexes. The nondenaturing detergent Triton X-100 is known to solubilize the AcChR in a form unable, upon binding of cholinergic ligands, to open the ion channel and to become desensitized. Solubilization of the AcChR in Triton X-100 affects the binding properties of this second site and converts it to a high-affinity, slowly reversible site. Prolonged incubation of M-AcChR at 4 degrees C converts the low-affinity site to a high-affinity site similar to those observed in the presence of Triton X-100. Although the two sites have similar properties when the AcChR is solubilized in Triton X-100, their nonequivalence can be demonstrated by the effect on alpha-BGT binding of concanavalin A, which strongly reduces the association rate of one site only. The Bmax of alpha-BGT to either Triton-solubilized AcChR or M-AcChR is not affected by the presence of concanavalin A. Occupancy of the high-affinity, slowly reversible site in M-AcChR inhibits the Triton X-100 induced conversion to irreversibility of the second site. At difference with alpha-BGT, the long alpha-neurotoxin from Naja naja siamensis venom (alpha-NTX) binds with high affinity and in a very slowly reversible fashion to two sites in the M-AcChR. We confirm here that Triton-solubilized AcChR or M-AcChR binds in a very slowly reversible fashion the same amount of alpha-NTX.

• OSTI ID: 6746985
• Journal Information: Biochemistry; (USA), Vol. 29:4; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
ACETYLCHOLINE
RECEPTORS
BIOCHEMICAL REACTION KINETICS
AFFINITY
CELL MEMBRANES
CONCANAVALIN
IODINE ISOTOPES
TOXINS
TRACER TECHNIQUES
ULTRACENTRIFUGATION
AMINES
AMMONIUM COMPOUNDS
ANTIGENS
AUTONOMIC NERVOUS SYSTEM AGENTS
CELL CONSTITUENTS
CENTRIFUGATION
DRUGS
ESTERS
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
MATERIALS
MEMBRANE PROTEINS
MEMBRANES
NEUROREGULATORS
ORGANIC COMPOUNDS
PARASYMPATHOMIMETICS
PROTEINS
QUATERNARY COMPOUNDS
REACTION KINETICS
SEPARATION PROCESSES
TOXIC MATERIALS
550201* - Biochemistry- Tracer Techniques