The molecular architecture of hemidesmosomes, as revealed with super-resolution microscopy

Hemidesmosomes have been extensively studied with immunofluorescence microscopy, but owing to its limited resolution, the precise organization of hemidesmosomes remains poorly understood. We studied hemidesmosome organization in cultured keratinocytes with two- and three-color super-resolution microscopy. We observed that, in the cell periphery, nascent hemidesmosomes are associated with individual keratin filaments and that beta4 integrin (also known as ITGB4) is distributed along, rather than under, keratin filaments. By applying innovative methods to quantify molecular distances, we demonstrate that the hemidesmosomal plaque protein plectin interacts simultaneously and asymmetrically with beta4 integrin and keratin. Furthermore, we show that BP180 (BPAG2, also known as collagen XVII) and BP230 (BPAG1e, an epithelial splice variant of dystonin) are characteristically arranged within hemidesmosomes with BP180 surrounding a central core of BP230 molecules. In skin cross-sections, hemidesmosomes of variable sizes could be distinguished with BP230 and plectin occupying a position in between beta4 integrin and BP180, and the intermediate filament system. In conclusion, our data provide a detailed view of the molecular architecture of hemidesmosomes in cultured keratinocytes and skin.