Output whole line once for each unique value of a column (Bash)

This must surely be a trivial task with `awk` or otherwise, but it's left me scratching my head this morning. I have a file with a format similar to this: ``` pep> AEYTCVAETK 2 genes ADUm.1024,ADUm.5198,ADUm.750 pep> AIQLTGK 1 genes ADUm.1999,ADUm.3560 pep> AIQLTGK 8 genes ADUm.1999,ADUm.3560 pep> KHEPPTEVDIEGR 5 genes ADUm.367 pep> VSSILEDKTT 9 genes ADUm.1192,ADUm.2731 pep> AIQLTGK 10 genes ADUm.1999,ADUm.3560 pep> VSSILEDKILSR 3 genes ADUm.2146,ADUm.5750 pep> VSSILEDKILSR 2 genes ADUm.2146,ADUm.5750 ``` I would like to print a line for each distinct value of the peptides in column 2, meaning the above input would become: ``` pep> AEYTCVAETK 2 genes ADUm.1024,ADUm.5198,ADUm.750 pep> AIQLTGK 1 genes ADUm.1999,ADUm.3560 pep> KHEPPTEVDIEGR 5 genes ADUm.367 pep> VSSILEDKTT 9 genes ADUm.1192,ADUm.2731 pep> VSSILEDKILSR 3 genes ADUm.2146,ADUm.5750 ``` This is what I've tried so far, but clearly neither does what I need: ``` awk '{print $2}' file | sort | uniq # Prints only the peptides... awk '{print $0, "\t", $1}' file |sort | uniq -u -f 4 # Altogether omits peptides which are not unique... ``` One last thing, It will need to treat peptides which are substrings of other peptides as distinct values (eg VSSILED and VSSILEDKILSR). Thanks :)