Abstract
Mammalian mitochondrial ribosomes possess a binding site for guanine nucleotides. GTP binds in unit stoichiometry and with high affinity (Kd = 15.3 +/- 2.8 nM) to the small subunit of bovine mitochondrial ribosomes. This binding activity survives high salt washes, indicating that the nucleotide binds to an integral site within this subunit. GDP also binds to the small subunit with high affinity (Kd = 17 +/- 5.8 nm) and in unit stoichiometry. The GTP binding activity can be competed with GDP but not appreciably by other nucleotides, indicating that both GTP and GDP bind specifically and to the same site. The non-hydrolyzable analogs of GTP, guanylyl-5'-imidophosphate, and guanylyl-(beta,gamma-methylene)- diphosphonate also bind to the small subunit, but with reduced affinity. These results indicate that mammalian mitochondrial ribosomes, unlike other ribosomes, are able to interact directly with guanosine triphosphate, suggesting that the bound GTP may be involved in a novel regulatory mechanism in mitochondrial protein synthesis.
Highlights
Mammalianmitochondrialribosomespossess a bind- basic and more hydrophobic than their bacterial’ or cytoingsite for guanine nucleotides
The above results indicate that the small subunit of mitochondrial ribosomes contains a high affinity binding site for the guanine nucleotides GTP and GDP
It is significant that these nucleotides bind under physiological ionic conditions, suggesting that GTP binds to mitochondrial ribosomes in uiuo
Summary
Vol 266, No 15, Issue of May 25, pp. 9586-9590,1991 Printed in U.S.A. Bovine Mitochondrial RibosomesPossess a HighAffinity Binding Site for Guanine Nucleotides*. GTP binds in unit plasmic (Matthews et al, 1982) counterparts These stoichiometry and with high affinity(& = 15.3 2 2.8 proteins show no obvious homology with other r-proteins as nM) to the small subunit ofbovine mitochondrialribo- detected by electrophoretic mobility, immunologic cross-resomes. This binding activity surviveshigh salt washes, activity, or limited amino acid sequence analysis’ (Matthews indicating that the nucleotide binds to an integral site et al, 1982). The costs of mitochondrial small and large ribosomal subunits could bind GTP and that thibsinding required neither exogenous factors publication of this article were defrayed in part by the payment of page charges.
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