Answer:
secondary structure
Step-by-step explanation:
Alpha helices and beta sheets are two main structural forms in secondary structure of proteins. This structures are formed spontaneously. The next step of protein structure formation is folding into tertiary three-dimensional form.
In diseases such as CJD and kuru, protein prion is changed in structure. It is not known how degeneration of priones protein structure occurs, but it can lead to neurodegenerative diseases which can even be fatal.
Priones are also known as proteinaceous infectious particles.