Effects of two photoreactive spermine analogues on peptide bond formation and their application for labeling proteins in Escherichia coli functional ribosomal complexes
I. Amarantos et al., Effects of two photoreactive spermine analogues on peptide bond formation and their application for labeling proteins in Escherichia coli functional ribosomal complexes, BIOCHEM, 40(25), 2001, pp. 7641-7650
The effect of two photoreactive analogues of spermine, N-1-azidobenzamidino
- (ABA-) spermine and N-1-azidonitrobenzoyl- (ANB-) spermine, on ribosomal
functions was studied in a cell-free system derived from Escherichia coli.
In the dark, both analogues stimulated the binding of AcPhe-tRNA to poly(U)
-programmed ribosomes, enhanced the stability of the ternary complex AcPhe-
tRNA poly(U) ribosome (complex C), and caused stimulatory and inhibitory ef
fects on peptidyltransferase activity. ABA-spermine exhibited more pronounc
ed effects than ANB-spermine. Each photoprobe was covalently attached after
irradiation to both ribosomal subunits and also to free rRNA isolated from
70S ribosomes. Photolabeled complex C showed a reactivity toward puromycin
, similar to that exhibited by complex C reacting reversibly with photoprob
es free in solution. The distribution of the incorporated radioactivity amo
ng the ribosomal components was determined under two experimental condition
s, one stimulating and the other inhibiting peptidyltransferase activity. U
nder both conditions, ABA-spermine was the strongest cross-linker. Upon sti
mulatory conditions, 14% of ABA-[C-14]spermine cross-linked to complex C wa
s bound to the protein fraction. The proteins primarily labeled were identi
fied as S3, S4, L2, L3, L6, L15, L17, and L18. Upon inhibitory conditions,
a higher percent of the incorporated radioactivity was found in ribosomal p
roteins, while the pattern of protein labeling was characterized by a remar
kable decrease of cross-linked proteins L2, L3, L6, L15, L17. and L18 and b
y an increase of cross-linked proteins S9, S18, L1, L16, L22, L23, and L27.
On the basis of these results and literature data, the involvement of sper
mine in the conformation and important functions of ribosomes is discussed.