Biostructural chemistry of magnesium ion: Characterization of the weak binding sites on tRNA sup Phe (yeast). Implications for conformational change and activity

Journal Article · Tue Jun 26 00:00:00 EDT 1990 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00477a021· OSTI ID:6290750

Reid, S S; Cowan, J A ^[1]

---

1. Ohio State Univ., Columbus (USA)

The thermodynamics and kinetics of magnesium binding to tRNA{sup Phe}(yeast) have been studied directly by {sup 25}Mg NMR. In 0.17 M Na{sup +}(aq), tRNA{sup Phe} exists in its native conformation and the number of strong binding sites was estimated to be 3-4 by titration experiments, in agreement with X-ray structural data for crystalline tRNA{sup Phe}. The set of weakly bound ions were in slow exchange and {sup 25}Mg NMR resonances were in the near-extreme-narrowing limit. The number of weak magnesium binding sites was determined to be 50 {plus minus} 8 in the native conformation and a total line-shape analysis of the exchange-broadened {sup 25}Mg{sup 2+} NMR resonance gave an association constant K{sub a} of (2.2 {plus minus} 0.2) {times} 10{sup 2} M{sup {minus}1}, a quadrupolar coupling constant ({chi}{sub B}) of 0.84 MHz, an activation free energy ({Delta}G{sup *}) of 12.8 {plus minus} 0.2 kcal mol{sup {minus}1}, and an off-rate (k{sub off}) of (2.5 {plus minus} 0.4) {times} 10{sup 3} s{sup {minus}1}. In the absence of background Na{sup +}(aq), up to 12 {plus minus} 2 magnesium ions bind cooperatively, and 73 {plus minus} 10 additional weak binding sites were determined. In comparison to Mg{sup 2+} binding to proteins the lower {chi}{sub B} values suggest a higher degree of symmetry for the ligand environment of Mg{sup 2+} bound to tRNA. A small number of specific weakly bound Mg{sup 2+} appear to be important for the change from a nonnative to a native conformation. Implications for interactions with the ribosome are discussed.

• OSTI ID: 6290750
• Journal Information: Biochemistry; (USA), Journal Name: Biochemistry; (USA) Vol. 29:25; ISSN 0006-2960; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550601* -- Medicine-- Unsealed Radionuclides in Diagnostics
62 RADIOLOGY AND NUCLEAR MEDICINE
ALKALINE EARTH ISOTOPES
CATIONS
CHARGED PARTICLES
CHEMICAL REACTIONS
CONFORMATIONAL CHANGES
CROSS-LINKING
EUMYCOTA
EVEN-ODD NUCLEI
FUNGI
IONS
ISOTOPES
LIGHT NUCLEI
MAGNESIUM 25
MAGNESIUM ISOTOPES
MAGNETIC RESONANCE
MICROORGANISMS
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUCLEIC ACIDS
ORGANIC COMPOUNDS
PLANTS
POLYMERIZATION
RESONANCE
RNA
STABLE ISOTOPES
TEMPERATURE DEPENDENCE
TRANSFER RNA
YEASTS