NCBI Homepage 
NCBI creates public databases, conducts research in computational biology, develops software tools for analyzing genome data, and disseminates biomedical information - all for the better understanding of molecular processes affecting human health and disease.

Structural Classification of Proteins (SCOP) 
Nearly all proteins have structural similarities with other proteins and, in some of these cases, share a common evolutionary origin. The SCOP database, created by manual inspection and abetted by a battery of automated methods, aims to provide a detailed and comprehensive description of the structural and evolutionary relationships between all proteins whose structure is known. As such, it provides a broad survey of all known protein folds, detailed information about the close relatives of any particular protein, and a framework for future research and classification.

The Knottin Web 
Database of small cysteine rich proteins known as the knottins.

The Protein Data Bank 
A single worldwide repository for the processing and distribution of 3-D biological macromolecular structure data.

PROSITE cyclotide motif
PROSITE describes sequence-based motifs in proteins

Orientations of Proteins in Membranes
OPM is a database of fitted spatial arrangments of proteins in membranes

Cylcotides - Wikipedia
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