* Roche signs deal with Prothena Corp.

* Roche looking to diversify beyond cancer drugs

* Prothena treatment likely to enter Phase I in 2014

ZURICH, Dec 12 (Reuters) - Roche has raised it bet on medicines for the human brain by signing a deal with Ireland's Prothena Corp worth up to $600 million to develop and commercialise a treatment for Parkinson's disease.

The Swiss drugmaker is looking to diversify beyond its core expertise in cancer and is also developing treatments for Alzheimer's disease, schizophrenia and multiple sclerosis among other neurodegenerative disorders.

Under the deal with Prothena, announced late on Wednesday, Roche will gain access to PRX022, a monoclonal antibody for the treatment of Parkinson's disease expected to enter Phase I clinical trials in 2014.

Prothena in turn will get a $45 million upfront payment and clinical milestone. It is entitled to further milestone payments of up to $555 million if it meets development, regulatory and commercial goals.

Prothena, which was spun out of Irish drugmaker Elan last December, will also receive 30 percent of the profits on U.S sales and will share 30 percent of the development and commercialisation costs.

Parkinson's disease is a debilitating condition where the brain gradually becomes damaged, leading to a worsening of motor functions. An estimated 7 to 10 million people live with the disease worldwide, Roche said.

"Currently, there is no treatment that modifies its course, and by targeting one of Parkinson's key molecular determinants, PRX002 has the potential to slow down or reduce its progression," said Luca Santarelli, head of neuroscience and small molecules research at Roche.

PRX002 works by targeting the protein alpha-synuclein which plays a part in several neurodegenerative disorders, including Parkinson's, dementia with Lewy bodies and neurodegeneration with brain iron accumulation.

The two companies may also work together to potentially develop PRX002 for other neurodegenerative disorders characterised by synuclein proteins.