Multiple sequence alignment. Convert multi-line format to single-line format? - bioinformatics

Question

I have a multiple sequence alignment file in which the lines from the different sequences are interspersed, as in the format outputed by clustal and other popular multiple sequence alignment tools. It looks like this:
TGFb3_human_used_for_docking ALDTNYCFRNLEENCCVRPLYIDFRQDLGWKWVHEPKGYYANFCSGPCPY
tr|B3KVH9|B3KVH9_HUMAN ALDTNYCFRNLEENCCVRPLYIDFRQDLGWKWVHEPKGYYANFCSGPCPY
tr|G3UBH9|G3UBH9_LOXAF ALDTNYCFRNLEENCCVRPLYIDFRQDLGWKWVHEPKGYYANFCSGPCPY
tr|G3WTJ4|G3WTJ4_SARHA ALDTNYCFRNLEENCCVRPLYIDFRQDLGWKWVHEPKGYYANFCSGPCPY
TGFb3_human_used_for_docking LRSADTTHST-
tr|B3KVH9|B3KVH9_HUMAN LRSADTTHST-
tr|G3UBH9|G3UBH9_LOXAF LRSTDTTHST-
tr|G3WTJ4|G3WTJ4_SARHA LRSADTTHST-
Each line begins with a sequence identifier, and then a sequence of characters (in this case describing the amino acid sequence of a protein). Each sequence is split into several lines, so you see that the first sequence (with ID TGFb3_human_used_for_docking) has two lines. I want to convert this to a format in which each sequence has a single line, like this:
TGFb3_human_used_for_docking ALDTNYCFRNLEENCCVRPLYIDFRQDLGWKWVHEPKGYYANFCSGPCPYLRSADTTHST-
tr|B3KVH9|B3KVH9_HUMAN ALDTNYCFRNLEENCCVRPLYIDFRQDLGWKWVHEPKGYYANFCSGPCPYLRSADTTHST-
tr|G3UBH9|G3UBH9_LOXAF ALDTNYCFRNLEENCCVRPLYIDFRQDLGWKWVHEPKGYYANFCSGPCPYLRSTDTTHST-
tr|G3WTJ4|G3WTJ4_SARHA ALDTNYCFRNLEENCCVRPLYIDFRQDLGWKWVHEPKGYYANFCSGPCPYLRSADTTHST-
(In this particular examples the sequences are almost identical, but in general they aren't!)
How can I convert from multi-line multiple sequence alignment format to single-line?

Answer 1

Looks like you need to write a script of some sort to achieve this. Here's a quick example I wrote in Python. It won't line the white-space up prettily like in your example (if you care about that, you'll have to mess around with formatting), but it gets the rest of the job done
#Create a dictionary to accumulate full sequences
full_sequences = {}
#Loop through original file (replace test.txt with your file name)
#and add each line to the appropriate dictionary entry
with open("test.txt") as infile:
for line in infile:
line = [element.strip() for element in line.split()]
if len(line) < 2:
continue
full_sequences[line[0]] = full_sequences.get(line[0], "") + line[1]
#Now loop through the dictionary and write each entry as a single line
outstr = ""
with open("test.txt", "w") as outfile:
for seq in full_sequences:
outstr += seq + "\t\t" + full_sequences[seq] + "\n"
outfile.write(outstr)