[BioC] BLAST E-value

[Alla Bulashevska]

Dear Bioconductor users,
i am doing cross-species analysis and searching for the way
how to pairwise align thousands of sequences efficiently. I
should become the BLAST E-value as output. 
The pairwiseAlignment in the Biostrings package can align
 two protein sequences but outputs Smith Watermann score.
I will appreciate it greatly if somebody can tell me, how
this score could be transferred into E-value.

Thank you for your help,
Alla.