I want to get all the miRNAs PDB structures from PDB. But When i do advance search in PDB, it gives me only 1 structure. SO, could anyone suggest me some database of miRNA from where i can download all the available PDB structures or all the miRNA structures from PDB?
You could try "Macromolecule Type" in advanced search and select "Yes" for RNA and "No" for the other options. You could also specify number of chains = 1 and select maximum/minimum lengths ("Chain Length") for typical miRNAs.
However, you'll have to do some manual filtering of the final result set, since "miRNA" does not seem to be a common annotation in the PDB.
It may also be that there simply are not very many miRNA structures (and they are likely to be solution NMR, rather than crystal structures).