In molecular biology, ADF-H domain (actin-depolymerising factor homology domain) is an approximately 150 amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 motif that is present in three phylogenetically distinct classes of eukaryotic actin-binding protein

Actin-binding protein

Actin-binding proteins are proteins that bind to actin. This may mean ability to bind actin monomers, or polymers, or both....

s.

• ADF/cofilins, which include ADF
  Actin depolymerizing factor
  Actin depolymerizing factors are a family of microfilament proteins.They are used to regulate actin assembly....
  
  , cofilin
  Cofilin
  ADF/cofilin is a family of actin-binding proteins which disassembles actin filaments.Three highly conserved and highly identical genes belonging to this family have been described in human and mice:...
  
  , destrin
  Destrin
  Destrin or DSTN is a protein which in humans is encoded by the DSTN gene. Destrin is a component protein in microfilaments....
  
  , actophorin, coactosin, depactin and glia maturation factors
  Glia maturation factor
  Glia maturation factor is a nerve growth factor implicated in nervous system development, angiogenesis and immune function.The structures of mouse glia maturation factors beta and gamma, solved by both crystallography and NMR, reveal similarities and critical differences with ADF-H domains and...
  
   (GMFs) beta and gamma. ADF/cofilins are small actin-binding protein
  Protein
  Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
  
  s composed of a single ADF-H domain. They bind both actin-monomers and filaments and promote rapid filament turnover in cells
  Cell (biology)
  The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
  
   by depolymerising/fragmenting actin filaments. ADF/cofilins bind ADP
  Adenosine diphosphate
  Adenosine diphosphate, abbreviated ADP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside adenosine. ADP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase adenine....
  
  -actin with higher affinity than ATP
  Adenosine triphosphate
  Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
  
  -actin and inhibit the spontaneous nucleotide
  Nucleotide
  Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
  
   exchange on actin
  Actin
  Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
  
   monomer
  Monomer
  A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...
  
  s

• Twinfilins, which are actin monomer-binding proteins
  Protein
  Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
  
   that are composed of two ADF-H domains
  Protein domain
  A protein domain is a part of protein sequence and structure that can evolve, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Many proteins consist of several structural...
  
  

• Abp1/Drebrins, which are relatively large proteins composed of an N-terminal ADF-H domain followed by a variable region and a C-terminal SH3 domain
  SH3 domain
  The SRC Homology 3 Domain is a small protein domain of about 60 amino acids residues first identified as a conserved sequence in the viral adaptor protein v-Crk and the non-catalytic parts of enzymes such as phospholipase and several cytoplasmic tyrosine kinases such as Abl and Src...
  
  . Abp1/Drebrins interact
  Protein-protein interaction
  Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...
  
   only with actin filaments and do not promote filament depolymerisation or fragmentation Although these proteins are biochemically distinct and play different roles in actin dynamics, they all appear to use the ADF-H domain for their interactions with actin.

The ADF-H domain consists of a six-stranded mixed beta-sheet in which the four central strands (beta2-beta5) are anti-parallel and the two edge strands (beta1 and beta6) run parallel with the neighbouring strands. The sheet is surrounded by two alpha-helices

Alpha helix

A common motif in the secondary structure of proteins, the alpha helix is a right-handed coiled or spiral conformation, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...

on each side .