Mutual Folding Induced by Binding (MFIB) database is a repository for protein complexes that are formed exclusively by intrinsically unstructured proteins (IUPs). As these proteins have no stable tertiary structure in their monomeric form, their folding is induced by the assembly of the complex.

IUPs in general perform functions vital to living organisms. They are typically deeply embedded in signaling and regulatory pathways, play pivotal roles in transcription, stress-response, host-pathogen interactions and the development of a wide range of pathological states.

Since the systematic study of IUPs has been undertaken, a wealth of information has been accumulated about their biological functions, mechanisms of action and their abundance in (especially higher order) living organisms. These information are integrated into a large number of fundamental databases, such as UniProt and are also collected in IUP-specific databases, such as DisProt, IDEAL or MobiDB.

Many functions IUPs fulfill depend on their interactions with other protein partners. Upon interaction with ordered proteins, IUPs generally adopt a stable structure in a process termed coupled-folding-and-binding. Such interacting sites of IUPs often recognize their partners via a linear motif and thus linear motif databases, such as ELM contain several bound IUP structures. In addition, binding sites in IUPs that interact with ordered proteins can be predicted from the protein sequence alone using various bioinformatics tools, such as ANCHOR or MoRFchibi System.

MFIB complements the research of IUP interactions by providing a curated and annotated set of complexes that are formed by IUPs alone. In these cases the emerging complex structure does not form on the template surface of an ordered protein. Instead, the folding of all participating protein partners happens at the same time, coupled to the interaction in a synergistic manner. MFIB serves as a collection of such protein complexes together with their structural and functional annotations, as well as links and literature references that describe the experimental verification of the mutual coupled-folding-and-binding process, that is a hallmark of the described complexes.