Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The basic SH3-binding motif 163PPSP165 of human securin locates at the C-terminal region of the protein (UniProt: O95997) and can be elongated to an extended motif 163PPSPVK168, which belongs to the class II SH3 binding motif (PxxPx+, where + refers to a positively charged residue) (12).
Category: