$ perl -E '
> $_ = q{1 AC2 34 TRP A 6 ALA A 7 ILE A 14 GLY A 15};
> @e = grep { ( ++ $i ) % 6 } split m{(\s+)};
> say join q{}, map { shift @e } 1 .. 5 while @e;'
1 AC2 34
TRP A 6
ALA A 7
ILE A 14
GLY A 15
$