Table 3. Functional and structural roles of amino acids in loop 6 of cyclotides from V. odorata.

Positiona	Residuesb	Incidencec (%)	Functional/structural comments
a	Cys†	100	Flanking cysteine at start of loop. Part of the cystine knot [20].
b	Tyr†, Thr, Lys*, Ala*	62	Typically a hydrogen bond donor or acceptor [38] stabilizing the cyclotide structure.
c	Arg, Lys, His*, Phe*†	48	Typically a solvent-exposed positively charged residue [38].
d	Asn†, Asp	90	Functional role in the cyclization mechanism [26,36,38,47,48].
e	Gly, Ser, Asp*†	90	Typically, a small and uncharged amino acid involved in the cyclization mechanism [47] as the N-terminal residue that forms a bond with the C-terminal asparagine/aspartic residue
f	Ile†, Leu, Thr*, Ser*	41	Typically, a hydrophobic residue believed to be involved in haemolytic activity [38].
g	Pro, Val*, Ser*, Phe*†	93	Typically, turn-inducing and involved in hydrophobic interactions with residues in loops 5 and 6 [38].
h	Cys†	100	Final cysteine of loop 6. Part of the cystine knot [20].

^aPosition in loop 6 as outlined on the structure of cycloviolacin O14 (PDB ID: 2GJ0) in Figure 8.

^bThe residues expressed in V. odorata cyclotides at these positions. Residues shown in boldface are the most common in this position; *indicates residues seen in fewer than 20% of cyclotides, and †indicates residue in cycloviolacin O25.

^cIncidence of the most common residue.