Check if string exist in non-consecutive lines in a given column - bash

Question

I have files with the following format:
ATOM 8962 CA VAL W 8 8.647 81.467 25.656 1.00115.78 C
ATOM 8963 C VAL W 8 10.053 80.963 25.506 1.00114.60 C
ATOM 8964 O VAL W 8 10.636 80.422 26.442 1.00114.53 O
ATOM 8965 CB VAL W 8 7.643 80.389 25.325 1.00115.67 C
ATOM 8966 CG1 VAL W 8 6.476 80.508 26.249 1.00115.54 C
ATOM 8967 CG2 VAL W 8 7.174 80.526 23.886 1.00115.26 C
ATOM 4440 O TYR S 89 4.530 166.005 -14.543 1.00 95.76 O
ATOM 4441 CB TYR S 89 2.847 168.812 -13.864 1.00 96.31 C
ATOM 4442 CG TYR S 89 3.887 169.413 -14.756 1.00 98.43 C
ATOM 4443 CD1 TYR S 89 3.515 170.073 -15.932 1.00100.05 C
ATOM 4444 CD2 TYR S 89 5.251 169.308 -14.451 1.00100.50 C
ATOM 4445 CE1 TYR S 89 4.464 170.642 -16.779 1.00100.70 C
ATOM 4446 CE2 TYR S 89 6.219 169.868 -15.298 1.00101.40 C
ATOM 4447 CZ TYR S 89 5.811 170.535 -16.464 1.00100.46 C
ATOM 4448 OH TYR S 89 6.736 171.094 -17.321 1.00100.20 O
ATOM 4449 N LEU S 90 3.944 166.393 -12.414 1.00 94.95 N
ATOM 4450 CA LEU S 90 5.079 165.622 -11.914 1.00 94.44 C
ATOM 5151 N LEU W 8 -66.068 209.785 -11.037 1.00117.44 N
ATOM 5152 CA LEU W 8 -64.800 210.035 -10.384 1.00116.52 C
ATOM 5153 C LEU W 8 -64.177 208.641 -10.198 1.00116.71 C
ATOM 5154 O LEU W 8 -64.513 207.944 -9.241 1.00116.99 O
ATOM 5155 CB LEU W 8 -65.086 210.682 -9.033 1.00115.76 C
ATOM 5156 CG LEU W 8 -64.274 211.829 -8.478 1.00113.89 C
ATOM 5157 CD1 LEU W 8 -64.528 211.857 -7.006 1.00111.94 C
ATOM 5158 CD2 LEU W 8 -62.828 211.612 -8.739 1.00112.96 C
In principle, column 5 (W, in this case, which represents the chain ID) should be identical only in consecutive chunks. However, in files with too many chains, there are no enough letters of the alphabet to assign a single ID per chain and therefore duplicity may occur.
I would like to be able to check whether or not this is the case. In other words I would like to know if a given chain ID (A-Z, always in the 5th column) is present in non-consecutive chunks. I do not mind if it changes from W to S, I would like to know if there are two chunks sharing the same chain ID. In this case, if W or S reappear at some point. In fact, this is only a problem if they also share the first and the 6th columns, but I do not want to complicate things too much.
I do not want to print the lines, just to know the name of the file in which the issue occurs and the chain ID (in this case W), in order to solve the problem. In fact, I already know how to solve the problem, but I need to identify the problematic files to focus on those ones and not repairing already sane files.
SOLUTION (thanks to all for your help and namely to sehe):
for pdb in $(ls *.pdb) ; do
hit=$(awk -v pdb="$pdb" '{ if ( $1 == "ATOM" ) { print $0 } }' $pdb | cut -c22-23 | uniq | sort | uniq -dc)
[ "$hit" ] && echo $pdb = $hit
done

Answer 1

For this particular sample:
cut -c22-23 t | uniq | sort | uniq -dc
Will output
2 W
(the 22nd column contains 2 runs of the letter 'W')

Answer 2

untested
awk '
seen[$5] && $5 != current {
print "found non-consecutive chain on line " NR
exit
}
{ current = $5; seen[$5] = 1 }
' filename

Answer 3

Here you go, this awk script is tested and takes into account not just 'W':
{
if (ln[$5] && ln[$5] + 1 != NR) {
print "dup " $5 " at line " NR;
}
ln[$5] = NR;
}