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A homotetramer is a protein complex made up of four identical subunits which are associated but not covalently bound. [3] Conversely, a heterotetramer is a 4-subunit complex where one or more subunits differ. [4] Examples of homotetramers include: enzymes like beta-glucuronidase (pictured) export factors such as SecB from Escherichia coli [5]
Depending on the direction of the strands or parts of a strand that form the tetrads, structures may be described as parallel or antiparallel. G-quadruplex structures can be computationally predicted from DNA or RNA sequence motifs, [ 11 ] [ 12 ] but their actual structures can be quite varied within and between the motifs, which can number ...
Guanine tetrads can also influence recombination, replication, and transcription. [1] [2] For instance, guanine tetrads are found in the promoter region of the Myc family of oncogenes. [10] They also function in immunoglobulin class switching and may play a role in the genome of HIV. [11] Guanine tetrads appear frequently in the telomeric ...
The SC protein scaffold stabilizes the physical pairing of homologous chromosomes by polymerizing between them during meiotic prophase. [2] During synapsis, autosomes are held together by the synaptonemal complex along their whole length, whereas for sex chromosomes , this only takes place at one end of each chromosome.
Proteins form by amino acids undergoing condensation reactions, in which the amino acids lose one water molecule per reaction in order to attach to one another with a peptide bond. By convention, a chain under 30 amino acids is often identified as a peptide, rather than a protein. [1]
Direct interaction of two nascent proteins emerging from nearby ribosomes appears to be a general mechanism for oligomer formation. [18] Hundreds of protein oligomers were identified that assemble in human cells by such an interaction. [18] The most prevalent form of interaction was between the N-terminal regions of the interacting proteins.
The rough secondary-structure content of a biopolymer (e.g., "this protein is 40% α-helix and 20% β-sheet.") can be estimated spectroscopically. [15] For proteins, a common method is far-ultraviolet (far-UV, 170–250 nm) circular dichroism. A pronounced double minimum at 208 and 222 nm indicate α-helical structure, whereas a single minimum ...
Proteins are often synthesized in an inactive precursor form; typically, an N-terminal or C-terminal segment blocks the active site of the protein, inhibiting its function. The protein is activated by cleaving off the inhibitory peptide. Some proteins even have the power to cleave themselves.