I have a set of strings, each has a single character "X"

```
c("KGDDQSXQGGAPDAGQE", "TEEDSEEVXEQK", "LTXTSGETTQTHTEPTGDSK", "IXTHNSEVEEDDMDK", "SXENPEEDEDQRNPAK", "XTAEHEAAQQDLQSK", "ATVIXHGETLRRTK", "XAVAREESGKPGAHVTVK", "YHTINGHNAEVXK", "XAAEDDEDDDVDTK")

```

I would like to get a character vector with each element having 11 characters, the center of the string is "X" and there is 5 characters from the string on each side. If there are no 5 characters on one of the sides, then "x" is added instead.

E.g.  

"KGDDQSXQGGAPDAGQE", becomes "GDDQSXQGGAP"

"TEEDSEEVXEQK", becomes "DSEEVXEQKxx"

"LTXTSGETTQTHTEPTGDSK", becomes "xxxLTXTSGET"