Delete space in a specific column using sed or cut

Question

I have file a.pdb as

ATOM      1  N   ARG     1     -19.794 -23.351   -9.550  1.00  0.00           N
ATOM      2  H1  ARG     1     -20.314 -23.948   -8.920  1.00  0.00           H
ATOM      3  H2  ARG     1     -18.811 -23.572   -9.490  1.00  0.00           H
ATOM      4  H3  ARG     1     -20.049 -23.660  -10.480  1.00  0.00           H
ATOM      5  CA  ARG     1     -20.087 -21.926   -9.380  1.00  0.00           C

I want to delete one space between field 7 and 8, without changing the format, but just shifting one character backwards. The Decimal points should appear in column 35, 43 and 51 (now they are on 35, 43 and 52).

Answer 1

sed -r 's/^(.{46}) /\1/' infile > outfile

Answer 2

Same thing with cut:

cut -c 1-46,48- < a.pdb