Editing Intermediate filament (section)

=== Types I and II – acidic and basic keratins ===
[[File:Epithelial-cells.jpg|thumb|right|[[Keratin]] intermediate filaments (stained red) around [[epithelium|epithelial cells]]]]
{{further|Cytokeratin}}
These proteins are the most diverse among IFs and constitute [[Type I cytokeratin|type I (acidic)]] and [[Type II cytokeratin|type II (basic)]] IF proteins. The many [[isoform]]s are divided in two groups:{{cn|date=April 2025}}
* '''epithelial keratins''' (about 20) in [[epithelial]] cells (image to right)
* '''trichocytic keratins''' (about 13) ([[hair keratin]]s), which make up [[hair]], [[Nail (anatomy)|nails]], [[Horn (anatomy)|horns]] and [[reptile|reptilian]] [[Scale (zoology)|scales]].

Regardless of the group, keratins are either acidic or basic. Acidic and basic keratins bind each other to form acidic-basic heterodimers and these heterodimers then associate to make a keratin filament.<ref name="interfil"/>

[[Cytokeratin]] filaments laterally associate with each other to create a thick bundle of ~50&nbsp;nm radius. The optimal radius of such bundles is determined by the interplay between the long range electrostatic repulsion and short range hydrophobic attraction.<ref>{{cite journal | vauthors = Haimov E, Windoffer R, Leube RE, Urbakh M, Kozlov MM | title = Model for Bundling of Keratin Intermediate Filaments | journal = Biophysical Journal | volume = 119 | issue = 1 | pages = 65–74 | date = July 2020 | pmid = 32533940 | doi = 10.1016/j.bpj.2020.05.024 | pmc = 7335914 | bibcode = 2020BpJ...119...65H | doi-access = free }}</ref> Subsequently, these bundles would intersect through junctions to form a dynamic network, spanning the cytoplasm of epithelial cells.{{cn|date=April 2025}}