perl tricky pattern matching

Hi all!
Suppose you have the following string of letters :

$string ='LPSTEOPRTRYERTRETR';
and you want to search for the following pattern inside the string:
$pattern= LP[SKTAQEHLDN][TA][GN][EDASTV] =>5/6
By saying 5/6, I mean that you can have one mismatch but still it must return success.
If you check the string above, it has L, P, S, T and then E. There is no G in the pattern, but I am ok with it...
So, my question is how can you set a threshold in pattern matching above which you will return success...